methods of preservation essay

Food Preservation: Methods and Their Importance

Food is an essential life requirement related to every function our body performs. It is a source of nutritional components like vitamins, minerals, essential oils, and antioxidants which benefit our health in every possible aspect.

But every food has its specific shelf-life and gets spoiled after harvesting or slaughtering. Based on spoilage, foods are; perishable: foods that deteriorate within 1- 5 days and need immediate freezing; semi-perishable: foods that don’t need immediate freezing and can be stored for 3 to 5 months; and non-perishable: foods stored for a much more extended period.

Further processing of foods helps to increase their shelf-life, prevent the growth of microorganisms, and preserve the food’s nutritional value, known as food preservation. The procedure includes altering atmospheric conditions, enzymatic reactions, chemical treatment, and food moisture.  

Table of Contents

Methods of Food Preservation

Food preservation is the natural or mechanical action performed on food to elongate its shelf life after harvesting or slaughtering. These procedures can reduce food deterioration by inhibiting microorganisms’ growth, enzymatic reactions, and auto-oxidation. 

Preservation by drying, dehydration, and fermentation is the oldest method, and cold treatment, heat treatment, blanching, irradiation, and canning are the modern methods.

Drying Methods

Food preservation by the drying method has been followed for centuries. Drying refers to removing water from a solid compound (meat, fruits, vegetables, and nuts). Sun drying, solar drying, and air drying are the most performed drying methods. In industry, drum drying, spray drying, vacuum drying, freeze drying, bed drying, and convection air drying are also performed. Drying removes food’s moisture and prevents the growth of yeast, bacteria, and mold, which are responsible for damaging food quality.

Dehydration Method

Dehydration removes moisture (water content) from solid or liquid. It differs from drying because the application of artificial heat under a controlled atmosphere is performed. It is also an old method of food preservation. Dehydration makes food lighter and smaller. Dehydrated foods are preferable during trekking and traveling. Example: Mango, Broccoli, Beets, Grapes, Chicken Fish, etc.,

Food Preservation by Fermentation

Preservation by Cold Treatment

Food preservation by cold treatment includes chilling, freezing, and refrigeration.

Chilling is the preservation method where storage of meals occurs in lower temperature, above its freezing point but below atmospheric temperature. The chilling temperature is −1℃ to +8℃, depending upon the variety of food. Chilling helps to preserve salads, pizza, seafood, and dairy products.

In freezing, the preservation of meals occurs by lowering its temperature below its freezing point. Freezing helps to preserve butter, ice cream, milk, nuts, and grains.

Preservation by refrigeration is when the meal’s temperature is maintained between 0℃ and 8℃. Refrigeration helps to preserve jam, jelly, pickle, and sauce.  

Food Preservation by Heat Treatment

Sterilization is a preservation method process where all the microorganisms and spores with minimal chances of causing spoilage are destroyed. Two methods do sterilization: i) Physical sterilization (cold sterilization, heat sterilization), ii) Chemical sterilization (gas sterilization, cold chemical sterilization). Meat, fish, cream, soup, and sauce are usually sterilized.

Preservation by Blanching

Blanching is a type of mild-heat treatment (usually on fresh harvest) where exposure of the foods to hot water or steam help to maintain their physical and physiological properties and extend the shelf-life. It is usually performed before freezing, canning, or drying. Hot steam is preferred over hot water or high temperature to avoid the side effects of blanching (protein denaturation, damage to tissue cells). High-temperature treatment can make fruits and vegetables lose their color. So, to avoid that, sodium carbonate or calcium oxide is added to blancher water. Broccoli, fennel, green beans, and asparagus spears are preserved by blanching.

Preservation by Irradiation

Food irradiation is a treatment method that exposes the food to ionizing radicals (x-ray, gamma ray, and electron beam). It helps to reduce the harmful bacteria and parasites which can cause spoilage. Beef, pork, poultry, lettuce, eggs, coffee, fresh fruits and vegetables, and spices are approved for irradiation by FDA. 

Food Preservation by Canning

Storing food in containers or jars by hermetically sealing (tightly closed to prevent air from entering) and sterilizing it with heat is canning. Canning prevents the growth of microorganisms and the activity of food enzymes that can spoil food. The containers are first sterilized, and the food is sealed by vacuum packaging. After that, the container is exposed to heat and cooled. Pressure canning, water bath canning, and steam canning are the methods of canning. Meat, dairy products, and sea foods are preserved by canning. 

Importance of Food Preservation

• Preventing microbial growth: Stored foods become a great nutritional medium for the growth and colonization of microorganisms. Preservation methods remove some growth-promoting components, like moisture, warmth, etc., from the food, making the storage longer. 
• Preserving nutritional components: Spoilage of foods degrades the quality of food. Applying preservative methods helps to maintain the dietary details of the food. Although some changes occur during preservation, the stored food is still nutritionally dense. 
• Preventing physical and chemical damage in food: Preservation methods help avoid auto-oxidation and enzymatic reactions that occur in the foods. Heat and moisture can also cause food spoilage, and applying preservation methods can protect from such damage.   
• Elongating shelf-life: Since food preservation methods help avoid spoilage of foods, they automatically elongate the shelf-life of perishable and semi-perishable foods. 
• Save money: Time and again, buying food is the most significant area to spend money. Storage of nutrition for a more extended period means having consumable foods for longer. It means less expense in food which can help save cash. 

Drawbacks of Food Preservation

Although food preservation is highly advantageous for long-term savings, it also has different drawbacks. Some of the disadvantages of methods of food preservation are as follows:

• Adding sugars and salts to preserve food can make the food unsuitable for consumption by people with different health conditions.
• Sometimes food preservation can lead to loss of nutrients as chemical and physical states may change after treatment with different preservation methods.
• Long-term use of preserved foods can lead to gastrointestinal disorders like gastritis and indigestion. 
• Handbook of Food Preservation – Cold [Internet]. [cited 2023Jan18]. Available from: http://www.cold.org.gr/library/downloads/Docs/Handbook%20of%20Food%20Preservation.PDF
•  Prokopov, Tsvetko & Tanchev, Stoyan. (2007). Methods of Food Preservation. 10.1007/978-0-387-33957-3_1. 
• UGA [Internet]. [cited 2023Feb5]. Available from: https://nchfp.uga.edu/publications/usda/GUIDE01_HomeCan_rev0715.pdf

Diksha Koirala

Diksha Koirala is a recent graduate student in Food Technology. She developed an interest in the relationship between microorganisms and the environment and their impact on the food and food industries. She is sharing her knowledge here to make the world understand microorganisms and the role it plays in our daily life.

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Writing on Preservation and Distribution of Food Essay (Article)

The world today is facing a significant increase in population thus the inability to provide an adequate diet for the expanding population, due to improper distribution of food. A food essay on food preservation is important to address this issue. In this food essay, I will address fundamental requirements a writer can consider.

When writing food preservation essays an individual is required to address several key points. These help to extensively tackle the given food essay topic.

The key points are:

• Provide information on the different types of foods available globally and their importance to the community in the food preservation essay. This is because the methods used in food preservation differ depending on the food to be preserved and the duration of preservation.
• The food essay should tackle the problems associated with food, for example, food spoilage, the causes of these spoilages and their long term solutions. Such a food essay can help create awareness on the subject in the community.
• To address the several different methods used in food preservation in the food essay and the effects of preservation on food appearance, taste and its quality.
• How food preservation affects our health, in terms of nutrition.

Researching a little on the subject is advisable for the food essay to be relevant, credible, and to be taken seriously by the readers. Food preservation being a subject affecting all ages, use of simple language and a broad explanation of the subject is crucial. There are several sources of information a writer can use to come up with a good report on the given food essay.

Therefore, addressing preservation as a food essay can help reduce post-harvest wastage and improve the food condition in the world.

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• Open access
• Published: 21 November 2017

A review on mechanisms and commercial aspects of food preservation and processing

• Sadat Kamal Amit 1   na1 ,
• Md. Mezbah Uddin 1   na1 ,
• Rizwanur Rahman 1 ,
• S. M. Rezwanul Islam 1 &
• Mohidus Samad Khan 1  

Agriculture & Food Security volume  6 , Article number:  51 ( 2017 ) Cite this article

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Food preservation involves different food processing steps to maintain food quality at a desired level so that maximum benefits and nutrition values can be achieved. Food preservation methods include growing, harvesting, processing, packaging, and distribution of foods. The key objectives of food preservation are to overcome inappropriate planning in agriculture, to produce value-added products, and to provide variation in diet. Food spoilage could be caused by a wide range of chemical and biochemical reactions. To impede chemical and microbial deterioration of foods, conventional and primitive techniques of preserving foods like drying, chilling, freezing, and pasteurization have been fostered. In recent years, the techniques to combat these spoilages are becoming sophisticated and have gradually altered to a highly interdisciplinary science. Highly advanced technologies like irradiation, high-pressure technology, and hurdle technology are used to preserve food items. This review article presents and discusses the mechanisms, application conditions, and advantages and disadvantages of different food preservation techniques. This article also presents different food categories and elucidates different physical, chemical, and microbial factors responsible for food spoilage. Furthermore, the market economy of preserved and processed foods has been analyzed in this article.

Foods are organic substances which are consumed for nutritional purposes. Foods are plant or animal origin and contain moisture, protein, lipid, carbohydrate, minerals, and other organic substances. Foods undergo spoilage due to microbial, chemical, or physical actions. Nutritional values, color, texture, and edibility of foods are susceptible to spoilage [ 1 ]. Therefore, foods are required to be preserved to retain their quality for longer period of time. Food preservation is defined as the processes or techniques undertaken in order to maintain internal and external factors which may cause food spoilage. The principal objective of food preservation is to increase its shelf life retaining original nutritional values, color, texture, and flavor.

The history of ‘Food Preservation’ dates back to ancient civilization when the primitive troupe first felt the necessity for preserving food after hunting a big animal, which could not be able to eat at a time. Knowing the techniques of preserving foods was the first and most important step toward establishing civilization. Different cultures at different times and locations used almost the similar basic techniques to preserve food items [ 2 ].

Conventional food preservation techniques like drying, freezing, chilling, pasteurization, and chemical preservation are being used comprehensively throughout the world. Scientific advancements and progresses are contributing to the evolution of existing technologies and innovation of the new ones, such as irradiation, high-pressure technology, and hurdle technology [ 3 , 4 , 5 ]. The processing of food preservation has become highly interdisciplinary since it includes stages related to growing, harvesting, processing, packaging, and distribution of foods. Therefore, an integrated approach would be useful to preserve food items during food production and processing stages.

At present, the global market of the processed food items is about 7 trillion dollars, which is gradually growing with time [ 6 ]. Rapid globalization and industrialization are the major contributing factors for the progress of food processing industries in different countries. An analysis of the UNIDO Industrial Statistics Database (2005) shows that food processing in developing countries is an auspicious component of the manufacturing sector, and the contribution of food processing industries to the national GDP increases with country’s national income [ 7 , 8 ].

This review paper presents the classification of food items and discusses different physical, chemical, and biological factors of food spoilage. The basics and advancements of different trivial and modern food preservation techniques, which are attributed to impede food spoilage and to yield longer shelf life, are discussed here along with their mechanisms, application conditions, advantages, and disadvantages. This article also reports the global market trend of preserved and processed food. Figure  1 summarizes a flow diagram showing various categories of foods, components of food spoilage mechanisms, food preserving and processing methods, and global market analysis of preserved foods. This review offers the researchers, technologists, and industry managements a comprehensive understanding that could be highly useful to develop effective and integrated food preservative methods and to ensure food safety.

Summary of the review on mechanisms and commercial aspects of food preservation and processing

Classification of foods

Foods can be broadly classified according to the shelf life, functions and nutrient value, and processing mechanisms (Fig. 2 ). Different categories of foods are summarized in Table  1 and briefly discussed in the following sections.

Classification of food, recreated from references [ 9 , 10 , 11 , 12 ]

Food categories based on shelf life

Food spoilage is a natural process; through this process, food gradually loses its color, texture, flavor, nutritional qualities, and edibility. Consumption of spoiled food can lead to illness and in the extreme situation to death [ 9 ]. Considering the self life, food items can be classified as perishable, semi-perishable, and non-perishable [ 10 ].

Perishable Foods that have shelf life ranging from several days to about three weeks are known as perishable. Milk and dairy products, meats, poultry, eggs, and seafood are the examples of perishable food items. If special preservation techniques are not apprehended, food items could be spoiled straight away [ 10 ].

Semi-perishable Different food items can be preserved for long time (about six months) under proper storage conditions. These foods are known as semi-perishable. Vegetables, fruits, cheeses, and potatoes are few examples of semi-perishable food items.

Non-perishable Natural and processed foods that have indefinite shelf life are called non-perishable food items. These foods can be stored for several years or longer. Dry beans, nuts, flour, sugar, canned fruits, mayonnaise, and peanut butter are few examples of non-perishable foods.

Food categories based on functions and nutrients

According to the functions to human body, food items can be categorized as: (a) body building and repairing foods, (b) energy-giving foods, (c) regulatory foods, and (d) protective foods. Depending on the nutrition value, food items can be classified as: (a) carbohydrate-rich foods, (b) protein-rich foods, (c) fat-rich foods, and (d) vitamin- and mineral-rich foods. Table  1 presents different food items according to their functions and nutrients.

Food categories based on extent and purpose of processing

Different food processing techniques are used by the food industries to turn fresh foods into food products. Foods can be classified into three major groups based on the extent and purpose of food processing [ 14 ]: (a) unprocessed or minimally processed foods, (b) processed culinary or food industry ingredients, and (c) ultra-processed food products. Classification of foods based on extent and purpose of processing is presented in Table  2 .

Food spoilage: mechanism

Food spoilage is the process in which food edibility reduces. Food spoilage is related to food safety [ 9 ]. The primitive stage of food spoilage can be detected by color, smell, flavor, texture, or food. Different physical, microbial, or chemical actions can cause food spoilage. These mechanisms are not necessarily mutually exclusive since spoilage caused by one mechanism can stimulate another. Temperature, pH, air, nutrients, and presence of different chemicals are the major factors for food spoilage [ 9 ]. Different factors that affect food spoilage are presented in Fig.  3 and briefly discussed in the following sections.

Key physical, microbial, and chemical factors affecting food spoilage [ 9 ]

Physical spoilage

Food spoilage due to physical changes or instability is defined as physical spoilage. Moisture loss or gain, moisture migration between different components, and physical separation of components or ingredients are the examples of physical spoilage [ 9 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. The key factors affecting physical spoilage are moisture content, temperature, glass transient temperature, crystal growth, and crystallization.

Moisture content

A frequent cause of degradation of food products is the change in their water content. It may occur in the form of water loss, water gain, or migration of water [ 25 ]. Moisture transfer in food is directly related to the water activity ( a w ) of food item [ 9 , 26 ]. Water activity ( a w ) is a thermodynamic property which is expressed as the ratio of the vapor pressure of water in a system to the vapor pressure of pure water at the same temperature [ 15 , 27 ]. Equilibrium relative humidity at the same temperature may also be used in lieu of pure water vapor pressure. Water activity in food products reduces with temperature. In general, water activity of foods at normal temperature is 1.0, whereas at −20 and −40 °C temperatures the water activities are 0.82 and 0.68, respectively [ 16 , 17 , 21 ].

Temperature

The effect of temperature is the most significant factor in the case of fruit and vegetable spoilage. There is an optimum temperature range for slow ripening and to maximize post-harvest life. Slow ripening also requires an optimum relative humidity along with optimum air movement around fruit and vegetable. Apparently, these optimum conditions are called modified atmospheres (MA). Temperature usually besets the metabolism of the commodities and contemporarily alters the rate of attaining desired MA [ 17 ]. Low temperature can also have a negative effect on foods that are susceptible to freeze damage. At a lower temperature, when food products become partially frozen, breakage in cells occurs which damages the product. Most tropical fruits and vegetables are sensitive to chilling injury. This generally occurs before the food product starts to freeze at a temperature in between 5 °C and 15 °C [ 9 ].

Glass transition temperature

Glass transition temperature ( T g ) effects the shelf life of food products. Solids in food items may exist in a crystalline state or in an amorphous metastable state. This phenomenon depends on the composition of solids, temperature, and relative humidity [ 18 ]. The amorphous matrix may exist either as a very viscous glass or as a more liquid-like rubber [ 19 ]. At glass transition temperature, changes occur from the glassy state to rubbery state. This is a second-order phase transition process, which is temperature specific for each food. The physical stability of foods is related to the glass transition temperature. Glass transition temperature ( T g ) depends strongly on concentration of water and other plasticizers [ 22 ]. When dry food products are kept in highly humid conditions, the state of food products changes due to glass transition phenomena [ 9 ].

Crystal growth and crystallization

Freezing can also contribute to food degradation. Foods, which undergo slow freezing or multiple freeze, suffer severely due to crystal growth. They are subject to large extracellular ice growth. Rapid freezing forms ice within food cells, and these foods are more stable than slow freezing processed foods [ 23 ]. To minimize large ice crystal growth, emulsifiers and other water binding agents can be added during freezing cycles [ 20 ].

Foods with high sugar content can undergo sugar crystallization either by moisture accumulation or by increasing temperature. As a consequence, sugar comes to the surface from inside, and a gray or white appearance is noticed. Staling of sugar cookies, graininess in candies, and ice creams are the results of sugar crystallization [ 9 ]. Sugar crystallization can be delayed by the addition of fructose or starch. Moreover, above the respective glass transition temperature, time plays a crucial role in sugar crystallization process of food items [ 24 ].

Microbial spoilage

Microbial spoilage is a common source of food spoilage, which occurs due to the action of microorganisms. It is also the most common cause of foodborne diseases. Perishable foods are often attacked by different microorganisms. The growth of most microorganisms can be prevented or lingered by adjusting storage temperature, reducing water activity, lowering pH, using preservatives, and using proper packaging [ 28 ].

Microorganisms involved in food spoilage

Microorganisms involved in food spoilage can be divided into three major categories, which are molds, yeasts, and bacteria. Table  3 presents the active conditions of different microorganisms that affect foods.

Factors affecting microbial spoilage

There are intrinsic and extrinsic factors that can affect microbial spoilage in foods [ 29 ]. The intrinsic properties of foods determine the expected shelf life or perishability of foods and also affect the type and rate of microbial spoilage. Endogenous enzymes, substrates, sensitivity of light, and oxygen are the primary intrinsic properties associated with food spoilage [ 33 ]. To control food quality and safety, these properties can be controlled during food product formulation [ 10 ]. Intrinsic factors of food spoilage include pH, water activity, nutrient content, and oxidation–reduction potential [ 9 , 10 , 29 ]. Extrinsic factors of food spoilage include relative humidity, temperature, presence, and activities of other microbes [ 9 , 29 ].

Chemical spoilage

Chemical and biochemical reactions occur naturally in foods and lead to unpleasant sensory results in food products. Fresh foods may undergo elementary quality changes caused by: (a) microbial growth and metabolism which results in pH changes, (b) toxic compounds, and/or (c) the oxidation of lipids and pigments in fat which results in undesirable flavors and discoloration [ 33 , 34 ]. Chemical spoilage is interrelated with microbial actions. However, oxidation phenomena are purely chemical in nature and also dependent on temperature variations [ 33 ].

In presence of oxygen, amino acids convert into organic acid and ammonia. This is the elementary spoilage reaction in refrigerated fresh meat and fish [ 29 ].

The term ‘rancidification’ is used to denominate lipids oxidation through which unsaturated fats (lipids) undergo reaction with oxygen [ 35 ]. The consequences in food items are color alteration, off-flavor, and toxic substances formation [ 9 ]. Rancidification can be catalyzed by the presence of metal oxides and exposure to light increases the reaction rate. After this reaction, carbonyl compounds, responsible for rancid taste of foods, are produced [ 35 ]. Figure  4 presents auto-oxidation of fatty acids (RH).

Auto-oxidation of fatty acids (RH) [ 35 ]

Proteolysis

Proteolysis, a ubiquitous and irreversible posttranslational modification, involves limited and highly specific hydrolysis of peptide and iso-peptide bonds of a protein. The entire phenomena require the presence of miscellaneous protease enzymes [ 36 ]. Different specialized proteases play a key role in various regulatory processes. Moreover, highly specific proteolytic events are associated with normal and pathological conditions [ 37 ]. Foods containing nitrogen compounds frequently incur this reaction. Proteins, after being incurred through proteolysis, eventually get converted into small-sized amino acids. The following reaction presents proteolysis mechanism:

Many of these peptides have stiff taste which can be bitter or sweet [ 35 ]. Table  4 presents the taste of various amino acids [ 38 ].

Putrefaction

Putrefaction refers to the series of anaerobic reactions through which amino acids detour to a mixture of amines, organic acids, and stiff-smelling sulfur compounds, such as mercaptans and hydrogen sulfide. This is a biochemical phenomenon as the presence of bacteria is exigent all through the process. Along with amino acids, indole, phenols, and ammonia are also formed due to protein putrefaction [ 39 ]. Most of these chemicals have displeasing odor. Putrefaction is quite common in meats and other protein-rich foods at temperatures greater than 15 °C. This elevated temperature facilitates microbial activities [ 35 , 39 ].

Maillard reaction

Non-enzymatic browning, which is also known also as Maillard reaction, is another primary cause of food spoilage. This reaction occurs in the amino group of proteins, or the amino acids present in foods. Color darkening, reducing proteins solubility, developing bitter flavors, and reducing nutritional availability of certain amino acids are the common outcomes of Maillard reaction. This reaction occurs during the storing of dry milk, dry whole eggs, and breakfast cereals [ 40 ].

Pectin hydrolysis

Pectins are complex mixtures of polysaccharides that make up almost one-third of the cell wall of dicotyledonous and some monocotyledonous plants [ 41 , 42 ]. Indigenous pectinases are synthesized or activated during ripening of fruits and cause pectin hydrolysis which softens the structure of food. Damages of fruits and vegetables by mechanical means may also activate pectinases and initiate microbial attack [ 35 ]. Pectin substances may also be de-esterified by the action of pectin methyl esterase. This esterification process is initiated in situ on damaged tissues, firm fruits, and vegetables by strengthening the cell walls and enhancing intercellular cohesion via a mechanism involving calcium. Metal ions catalyze the decomposition of heat-labile fruit pigments, which consist of pectin ingredients. This process causes the color change in fruit jams or jellies [ 42 ]. Therefore, jams and jellies are preserved in glass containers rather than metallic jars.

Hydrolytic rancidity

Hydrolytic rancidity causes lipid degradation by the action of lipolytic enzymes. In this reaction, free fatty acids are cleaved off triglyceride molecules in the presence of water. These free fatty acids have rancid flavors or odor [ 9 ]. The released volatile fatty acids have a stiff malodor and taste; therefore, hydrolytic rancidity is extremely noticeable in fats, such as butter [ 43 ].

Food preserving and processing methods

Food preservation refers to the process or technique undertaken in order to avoid spoilage and to increase shelf life of food [ 44 , 45 ]. Different preservation and processing techniques are presented in Fig.  5 [ 46 , 47 , 48 ].

Classification of food preservation and processing methods, recreated from references [ 46 , 47 , 48 ]

Physical processing

Drying or dehydration is the process of removing water from a solid or liquid food by means of evaporation. The purpose of drying is to obtain a solid product with sufficiently low water content. It is one of the oldest methods of food preservation [ 49 ]. Water is the prerequisite for the microorganisms and enzymes to activate food spoilage mechanisms. In this method, the moisture content is lowered to the point where the activities of these microorganisms are inhibited [ 29 , 50 ]. Most microorganisms can grow at water activity above 0.95. Bacteria are inactive at water activity below 0.9. Most of the microorganisms cannot grow at water activity below 0.88 [ 51 , 52 ].

Drying has numerous advantages. It reduces weight and volume of foods, facilitates foods storage, packaging, and transportation, and also provides different flavors and smells. With all these benefits, drying is apparently the cheapest method of food preservation [ 53 ]. However, this process also has limitations. In some cases, significant loss of flavor and aroma has been observed after drying. Some functional compounds like vitamin C, thiamin, protein, and lipid are also lost because of drying [ 54 , 55 , 56 ].

Classification of drying Drying can be classified into three major groups: convective, conductive, and radiative. Convective drying is the most popular method to obtain over 90% dehydrated foods. Depending on the mode of operation, dryers can be classified as batch or continuous. For smaller-scale operations and short residence times, batch dryers are preferred. Continuous method of drying is preferential when long periodic operations are required and drying cost is needed to curtail [ 57 ].

Drying of different foods Food items, such as fruits, vegetables, meats, and fishes, are processed by drying. Instant coffee and tea are also produced by spray drying or freeze drying [ 58 , 59 ]. Processing temperature and drying time of different food items are presented in Table  5 .

Pasteurization Pasteurization is a physical preservation technique in which food is heated up to a specific temperature to destroy spoilage-causing microorganisms and enzymes [ 64 , 65 ]. Almost all the pathogenic bacteria, yeasts, and molds are destroyed by this process. As a result, the shelf life of food increases [ 66 , 67 ]. This process was named after the French scientist Louis Pasteur (1822–1895), who experimented with this process in 1862. He used this process to treat wine and beer [ 68 ]. Table  6 presents the applications of pasteurization process to preserve different food items.

Pasteurization techniques The efficiency of pasteurization depends on the temperature–time combination. This combination is mostly based on the thermal death-time studies of heat-resisting microorganisms [ 55 ]. On the basis of temperature and heat exposure, pasteurization can be categorized as vat (batch), high temperature short time (HTST), and ultra-high temperature (UHT); HTST and UHT are continuous processes [ 16 , 69 ]. Vat pasteurizer is suitable for small plants having the capacity of 100–500 gallons [ 56 ]. Vat pasteurization requires constant supervision to prevent overheating, over holding, or burning [ 44 ]. High-temperature short-time (HTST) pasteurization is a continuous process pasteurizer equipped with sophisticated control system, pump, flow diversion devices or valves, and heat exchanger equipment [ 56 ]. HTST pasteurization is also known as ‘flash pasteurization’ [ 56 , 70 ]. Vat and HTST pasteurization perishes pathogenic microorganisms effectively. However, to inactivate thermo-resisting spores ultra-high temperature (UHT) pasteurization is more effective than VAT and HTST [ 55 ]. During heat treatment of food items, minimal physical, chemical, or biological changes take place [ 71 ]. After heating is done, the products are aseptically packaged in sterile containers [ 46 ]. UHT pasteurized products have a longer shelf life than other pasteurized products. Table  7 presents the comparisons between the three pasteurization methods.

High heat of pasteurization process may damage some vitamins, minerals, and beneficial bacteria during pasteurization. At pasteurization temperature, Vitamin C is reduced by 20 per cent, soluble calcium and phosphorus are reduced by 5 per cent, and thiamin and vitamin B12 are reduced by 10 per cent. In fruit juices, pasteurization causes reduction in vitamin C, ascorbic acid, and carotene. However, these losses can be considered minor from nutritional point of view [ 44 , 72 ].

Thermal sterilization

Thermal sterilization is a heat treatment process that completely destroys all the viable microorganisms (yeasts, molds, vegetative bacteria, and spore formers) resulting in a longer period of shelf life [ 44 ]. Retorting and aseptic processing are two categories of thermal sterilization [ 44 , 73 ]. Thermal sterilization is different from pasteurization. Comparison of different criteria between pasteurization and sterilization is given in Table  8 .

Retorting is defined as the packaging of food in a container followed by sterilization [ 73 ]. Foods with pH above 4.5 require more than 100 °C as sterilization temperature. The attainment of such temperature can be possible in batch or continuous retorts. Batch retorts are gradually being superseded by continuous systems [ 75 ]. Hydrostatic retorts and rotary cookers are the most common continuous systems used in food industries [ 76 ]. Table  9 presents different criteria of batch and continuous retorts.

Aseptic packaging

Aseptic packaging involves placing commercially sterilized food in a sterilized package which is then subsequently sealed in an aseptic environment [ 79 ]. Conventional aseptic packaging utilizes paper and plastic materials. Sterilization can be achieved either by heat treatment, by chemical treatment, or by attributing both of them [ 79 ]. Aseptic packaging is highly used to preserve juices, dairy products, tomato paste, and fruit slices [ 75 ]. It can increase the shelf life of food items to a large extent; as an example, UHT pasteurization process can extend the shelf life of liquid milk from 19 to 90 days, whereas combined UHT processing and aseptic packaging extend shelf life to six months or more. Packages used for aseptic processing are produced from plastics having relative softening temperature. Moreover, aseptic filling can accept a wide range of packaging materials including: (a) metal cans sterilized by superheated steam, (b) paper, foil, and plastic laminates sterilized by hot hydrogen peroxide, and (c) a variety of plastic and metal containers sterilized by high-pressure steam [ 80 ]. Wide variation of packages thus enhances proficiency of aseptic packaging and diminishes cost.

The direct approach of aseptic packaging comprises of steam injunction and steam infusion. On the other hand, indirect approach of aseptic packaging includes exchanging heat through plate heat exchanger, scrapped surface heat exchanger, and tubular heat exchanger [ 81 ]. Steam injection is one of the fastest methods of heating and often removes volatile substances from some food products. On the contrary, steam infusion offers higher control over processing conditions than steam injection and minimizes the risk of overheating products. Steam infusion is suitable to treat viscous foods [ 81 ]. Tubular heat exchangers are adopted for operations at higher pressures and flow rates. These exchangers are not very flexible to withstand production capacity alteration, and their use is only limited to low viscous foods. Plate exchangers, on the other hand, overcome these problems. However, frequent cleaning and sterilizing requirements have made this exchanger less popular in food industries [ 81 ].

Freezing slows down the physiochemical and biochemical reactions by forming ice from water below freezing temperature and thus inhibits the growth of deteriorative and pathogenic microorganisms in foods [ 82 , 83 ]. It reduces the amount of liquid water in the food items and diminishes water activity [ 84 ]. Heat transfer during freezing of a food item involves a complex situation of simultaneous phase transition and alteration of thermal properties [ 85 ]. Nucleation and growth are two basic sequential processes of freezing. Nucleation means the formation of ice crystal, which is followed by ‘growth’ process that indicates the subsequent increase in crystal size [ 58 ].

Freezing time Freezing time is defined as the time required to lower the initial temperature of a product to a given temperature at its thermal center. In general, slow freezing of food tissues results in the formation of larger ice crystals in the extracellular spaces, while rapid freezing produces small ice crystals distributed throughout the tissue [ 85 ]. The International Institute of Refrigeration (1986) defines various factors of freezing time in relation to the food products and freezing equipment. Dimensions and shapes of the product, initial and final temperature, temperature of refrigerating medium, surface heat transfer coefficient of the product, and change in enthalpy and thermal conductivity of the product are the most important factors among them [ 16 ].

Individual quick freezing Individual quick freezing (IQF) generally relates to quick freezing of solid foods like green peas, cut beans, cauliflower pieces, shrimps, meat chunks, and fish. On the other hand, freezing related to liquid, pulpy or semiliquid products, like fruit juices, mango pulps, and papaya pulps is known as quick freezing. The ice crystals formed by quick freezing are much smaller and therefore cause less damage to cell structure or texture of the food. Shorter freezing period impedes the diffusion of salts and prevents decomposition of foods during freezing. IQF also allows higher capacity for commercial freezing plants with the resultant cost reduction. However, higher investment is required to set up a quick freezing plant [ 86 ]. Different quick freezing techniques, such as contact plate freezing, air-blast freezing, and cryogenic freezing, are used to process food items. The comparison between different quick freezing techniques for fishery products is presented in Table  10 .

In chilling process, the temperature of foods is maintained between −1 and 8 °C. Chilling process reduces the initial temperature of the products and maintains the final temperature of products for a prolonged period of time [ 88 ]. It is used to reduce the rate of biochemical and microbiological changes and also to extend shelf life of fresh and processed foods [ 89 ]. In practice, freezing process is often referred to chilling, when cooling is conducted at <15 °C [ 90 ]. Partial freezing is applied to extend the shelf life of fresh food items in modern food industries. This process reduces ice formation in foods, known as super chilling [ 91 ].

Chilling can be done by using various equipments, such as continuous air cooler, ice bank cooler, plate heat exchanger, jacketed heat exchanger, ice implementation system, vacuum attribution system, and cryogenic chamber [ 92 ]. Chilling rate is mainly dependent on thermal conductivity, initial temperature of foods, density, moisture content, presence or absence of a lid on the food storage vessel, presence of plastic bags as food packaging equipment, and the size as well as weight of food units [ 93 ]. Table  11 describes various methods for chilling solid and liquid food items.

Advantages and disadvantages of chilling Chilling storage is extensively used for its effective short-term preservation competency. Chilling retards the growth of microorganisms and prevents post-harvest metabolic activities of intact plant tissues and post-slaughter metabolic activities of animal tissues. It also impedes deteriorative chemical reactions, which include enzyme-catalyzed oxidative browning, oxidation of lipids, and chemical changes associated with color degradation. It also slows down autolysis of fish, causes loss of nutritive value of foods, and finally bares moisture loss [ 90 ]. Chilling is high capital intensive since this process requires specialized equipment and structural modifications. Chilling may reduce crispiness of selected food items [ 95 ]. Chilling process also dehydrates unwrapped food surfaces, which is a major limitation of chilling process [ 96 ].

Irradiation

Irradiation is a physical process in which substance undergoes a definite dose of ionizing radiation (IR) [ 97 ]. IR can be natural and artificial. Natural IR generally includes X-rays, gamma rays, and high-energy ultraviolet (UV) radiation; artificially generated IR is accelerated electrons and induced secondary radiation [ 98 , 99 ]. IR is used in 40 different countries on more than 60 different foods [ 97 ]. The effects of IR include: (a) disinfestation of grains, fruits, and vegetables, (b) improvement in the shelf life of fruits and vegetables by inhibiting sprouting or by altering their rate of maturation and senescence, and (c) improvement in shelf life of foods by the inactivation of spoilage organisms and improvement in the safety of foods by inactivating foodborne pathogens [ 100 , 101 ]. Different factors of food irradiation techniques are listed in Table  12 .

Regulatory limits of irradiation The IR dose delivered to foods is measured in kilo grays (kGy). 1 gray is equivalent to ionizing energy dose absorbed by 1 kg of irradiated material. IR regulatory limits are set by the legislative bodies. Depending on the regulatory authority, these limits may be expressed as minimum dose, maximum dose, or approved dose range [ 98 ]. Table  13 presents different regulatory limits for food irradiation applications.

Effects of Irradiation The nutritional parameters, such as lipids, carbohydrates, proteins, minerals, and most vitamins, remain unaffected by IR even at high doses [ 102 ]. At a high dose, IR may cause the loss of some micronutrients, most notably vitamins A, B1, C, and E. According to FDA, IR has effects on food nutritive value that is similar to those of conventional food processing techniques [ 102 ].

High-pressure food preservation

High hydrostatic pressure or ultra-high pressure processing (HPP) technology involves pressure attribution up to 900 MPa to kill microorganisms in foods. This process also inactivates spoilage of foods, delays the onset of chemical and enzymatic deteriorative processes, and retains the important physical and physiochemical characteristics of foods. HHP has the potential to serve as an important preservation method without degrading vitamins, flavors, and color molecules during the process [ 58 , 103 , 104 ]. Freshness and improved taste with high nutritional value are the peerless characteristics of HPP technology. This process is also environmental friendly, since energy consumption is very low and minimal effluents are required to discharge [ 105 , 106 ]. The major drawback of this technology is the high capital cost. In addition, limited information and skepticism about this technology also limit the wide application of HPP processes [ 58 , 78 , 105 ].

Mechanism and working principle HP process follows Le Chatelier’s principle and isostatic principle [ 58 ]. According to Le Chatelier’s principle, biochemical and physicochemical phenomena in equilibrium are accompanied by the change in volume and hence influenced by pressure. Regardless of the shape, size, or geometry of the products, the isostatic principle relies on the instant and uniform pressure transmittance throughout food systems [ 58 ]. HP processes affect all reactions and structural changes where a change in volume is involved. The combined effect of breaking down and permeabilization of cell membrane kills or inhibits the growth of microorganisms. Vegetative cells are inactivated at 3000 bar pressure (approximate) at ambient temperature, while spore inactivation requires much higher pressure in combination with the temperature rise to 60 °C to 70 °C. Moisture level is extremely important in this context since little effect is noticeable below 40% moisture content [ 81 ]. Container processing and bulk processing are two methods of preserving foods under high pressure. Table  14 presents the advantages and limitations of in-container and bulk processing of foods under high pressure.

Pulsed electric field

Pulsed electric field (PEF) food processing is defined as a technique in which food is placed between two electrodes and exposed to a pulsed high voltage field (20–40 kV/cm). Generally, the PEF treatment time is less than one second [ 84 ]. Low processing temperature and short residence time of this process allow a highly effective inactivation of microorganisms [ 107 ]. PEF processing is much effective to destroy gram-negative bacteria than gram-positive bacteria. Vegetative cells are much sensitive than spores to this process. All cell deaths occur due to the disruption of cell membrane function and electroporation [ 29 ]. PEF technology retains taste, flavor, and color of the foods. Furthermore, this technique is not toxic [ 108 ]. However, this process has no impact on enzymes and spores. It is also not suitable for conductive materials and only effective to treat liquid foods. This process is energy extensive and may possess environmental risks [ 72 , 109 ].

Preservation of liquid foods Nonthermal food preservation processes, such as HPP and PEF, are reported to be more effective than thermal processing [ 110 , 111 , 112 ]. Microbial inactivation achieved by PEF mainly depends on electric field strength (20–40 kV/cm) and number of pulses produced during processing [ 112 ]. It has been found that most of the spoilage and pathogenic microorganisms are sensitive to PEF. However, it is noted that treatment of plant or animal cells require a high field strength and higher energy input, which increases the processing cost. In addition, this kind of field strength may destroy the structure of solid food. Therefore, PEF is more favorable to preserve liquid foods. Microbial inactivation by PEF has been found effective for fruit or vegetable juices, milk, liquid egg, and nutrient broth [ 107 ].

Processing parameters Different types of foods are processed using PEF process. Processing parameters of different PEF-treated foods are listed in Table  15 .

Biological process: fermentation

Fermentation method uses microorganisms to preserve food. This method involves decomposition of carbohydrates with the action of microorganisms and/or the enzymes [ 113 ]. Bacteria, yeasts, and molds are the most common groups of microorganisms involved in fermentation of a wide range of food items, such as dairy products, cereal-based foods, and meat products [ 114 , 115 ]. Fermentation enhances nutritional value, healthfulness, and digestibility of foods. This is a healthy alternative of many toxic chemical preservatives [ 116 ].

Classification of fermentation Fermentation can be spontaneous or induced. There are different types of fermentation used in food processing. Mechanisms of different food fermentation techniques are briefly discussed below:

Alcohol fermentation is the result of yeast action on the simple sugar called ‘hexose’ converting this into alcohol and carbon dioxide. The quality of fermented products depends on the presence of alcohol. In this process, air is excluded from the product to avoid the action of aerobic microorganisms, such as the acetobacter. This process ensures the longer shelf life of the products. The following equation illustrates alcohol fermentation by conversion of hexose [ 117 ]

Vinegar fermentation takes place after alcohol fermentation. Acetobacter converts alcohol to acetic acid in the presence of excess oxygen [ 114 , 118 ]. Under this method, food products are preserved as pickles, relishes, etc. [ 104 ]. Vinegar fermentation results in acetic acid and water by oxidation of alcohol [ 114 ]

Lactic acid fermentation takes place due to the presence of two types of bacteria: homofermenters and heterofermenters. Homofermenters produce mainly lactic acid, via the glycolytic (Embden–Meyerhof pathway). Heterofermenters produce lactic acid plus appreciable amounts of ethanol, acetate, and carbon dioxide, via the 6-phosphogluconate/phosphoketolase pathway [ 114 ].

Homolactic fermentation—The fermentation of 1 mol of glucose yields two moles of lactic acid

Heterolactic fermentation—The fermentation of 1 mol of glucose yields 1 mol each of lactic acid, ethanol, and carbon dioxide [ 114 ]

In the fermentation process, different kinds of microorganisms are used exclusively to produce flavor in foods, which are presented in Table  16 [ 113 ].

Chemical processes

Food preservation using chemical reagents is one of the ancient and traditional methods [ 119 ]. Effectiveness of this method depends on the concentration and selectivity of the chemical reagents, spoilage-causing organisms, and the physical and chemical characteristics of food items [ 120 ]. The global consumption and application of food additives and preservatives are extending. At present (2012 data), North America dominated the food preservative market followed by Asia–Pacific. It is expected that the food preservative market will reach to a volume of $2.7 billion by the end of 2018 [ 121 ]. However, using chemical reagents as food additives and preservatives is a sensitive issue because of health concerns [ 122 ]. In different countries, the applications chemical preservatives and food additives are monitored and regulated by different acts, rules, and government authorities [ 119 , 123 , 124 ].

Chemical preservatives

Preservatives are defined as the substances capable of inhibiting, retarding, or arresting the growth of microorganisms or any other deterioration resulting from their presence [ 125 ]. Food preservatives extend the shelf life of certain food products. Preservatives retard degradation caused by microorganisms and therefore maintain the color, texture, and flavor of the food item [ 125 ].

Food preservatives can be classified as natural and artificial. Animals, plants, and microorganisms contain various chemicals which have potential to preserve foods. They also function as antioxidants, flavorings, and antibacterial agents [ 126 ]. Table  17 presents different natural reagents with their functions as food preservatives. Artificial preservatives are produced industrially. These can be classified as antimicrobial, antioxidant, and antienzymatic [ 127 ]. The classification of artificial preservatives used in food industry is presented in Table  18 .

Food additives

The key objectives to use food additives are to improve and maintain nutritional value, to enhance quality, to reduce wastage, to enhance customer acceptability, to make food more readily available, and to facilitate processing food items [ 131 ]. Food additives can be either natural or synthetic chemical substances that are used intentionally during processing, packaging, or storage of foods to bring desired changes in food characteristics. Food additives can be divided into two major groups: intentional and incidental. Among these two, intentional additives are strictly controlled by government authority [ 131 ]. According to the National Academy of Sciences (1973), additives are prohibited to disguise faulty process, to hide spoilage, damage, or other inferiority, and apparently to deceive consumer. Moreover, if additives cause substantial reduction in nutrition, then their uses are also unaffiliated [ 131 ]. Table  19 presents different types of food additives with their possible applications.

Possible health effects of food additives and preservatives

Chemical food additives and preservatives are mostly considered safe, but several of them have negative and potentially life-threatening side effects. For example, nitrates, upon ingestion, are converted to nitrites that can react with hemoglobin to produce met-hemoglobin (aka: met-hemoglobin), a substance that can cause loss of consciousness and death, especially in infants. Different artificial food colorings, such as tartrazine, allura red, ponceau, and benzoate preservatives, have adverse effects on the behavior of infants; these additives are credited as the cause of the hyperactive behaviors of infants [ 133 ]. Preservatives also have intolerances among people who have asthma. Sulfites (including sodium bisulfite, sodium meta-bisulfite, and potassium bisulfite) found in wine, beer, and dried fruits are known to trigger asthmatic syndromes and cause migraines in people who are sensitive to them. Sodium nitrate and sodium nitrite are also classified as ‘probable carcinogenic elements’ to humans by International Agency for Research of Cancer (IARC) [ 134 ]. Nitrites and benzoates may have adverse effects on pregnant women. Sodium nitrite intake lowers hemoglobin and hematocrit values of pregnant women. Both benzoate and nitrite induce decrease in serum bilirubin and increase in serum urea. Consequently, the mean weight and length of the fetus get lowered [ 135 ]. Nitrites, after ingestion, get converted into nitrosamines, which could be harmful to a fetus [ 136 ]. Table  20 discusses the excerpts of negative effects of harmful food preservatives.

Analysis of market economy of preserved foods: global perspective

Food processing industries hold a dominating position in global economy. The processed food market is undergoing constant growth due to technological advancements, increasing demand, and the taste and behavioral pattern of consumers. Both developed and developing countries are opting new food processing and distribution methods responding to this progress [ 142 , 143 , 144 ].

The global fruit and vegetable processing industry is expected to grow at an accelerated pace in the upcoming years. Domestic demand for industry products is expected to grow particularly strong, specifically in developing economies, such as China and India. On the other hand, demand in developed economies (such as the USA) is expected to decline at a marginal rate as consumers increasingly replace their consumption of processed fruits and vegetables with fresh produce. Trade in processed fruit and vegetable products is expected to grow at an annualized rate of 3.3% in the next five years (2016–2021); the overall industry revenue is expected to grow at an annualized rate of 3.0% (2016–2021) [ 145 ]. Figure  6 represents the present and future trend of vegetable and fruit processing industries in the world.

Present and future trend of vegetable and fruit processing industries [ 145 ]

The developing world produces majority of the world’s fresh fruits and vegetables [ 145 ]. According to data sourced from the Food and Agriculture Organization of the United Nations, China produces about half of the world’s vegetables and one-third of the world’s fruits [ 142 , 145 ]. The production of processed fruits and vegetables occurs in all regions of the globe. However, high-tech, large-scale fruit and vegetable processing operations are concentrated primarily in Europe and Asia [ 145 ]. Table  21 represents the contribution of different regions in global processed fruit and vegetable production. Many leading fresh product producing countries often import fresh products from separate countries to meet the demand of their food processing industries. Production in developing nations is also growing to meet the demand of growing population. As a result, the number of industry enterprises and workers are forecast to grow at annualized rates of 2.2 and 1.6%, respectively, till 2017 [ 145 , 146 ]. After 2019–2020, a decline in the growth of global vegetable and food processing industries is anticipated (Fig.  6 ) because of the following possible reasons [ 118 , 145 , 146 ]:

Global vegetable and food processing industries are expected to face fierce competition from substitute foods, such as fresh fruit and vegetables;

Technological change will be relatively minimal and focused on improving processing efficiency; and

Industry product categories will be well defined with relatively minimal product innovation.

The chilled food market has been showing an upward trend throughout the world, and it reached to a size of 57 billion kilograms in 2015 worth of 11.4 billion euros [ 108 ]. Chilled food products include chilled fish/seafood, chilled pizza, chilled ready meals, chilled fresh pasta, sandwiches, salads, chilled meat products, and deli food which includes cured, fermented, and cooked meals [ 147 ]. The UK chilled food market had a growth rate of 3.6% in 2014 and expected to grow more than 15% over the next five years [ 148 ]. The US frozen food market revenue is expected to reach 70 billion USD by the end of 2024 [ 106 ].

Milk and alcoholic beverages mostly constitute pasteurized food market [ 149 ]. Presently, almost all the countries consume pasteurized liquid milk. Pasteurized milk constitutes 70% of global liquid milk market [ 150 ].

The world beverage market is expected to have an annual growth rate of 1.5% in 2015 [ 151 ]. In USA, the total beverage industry was more than USD $1.2 trillion [ 152 ]. Asia’s beverage market is expected to experience unprecedented growth as well by taking two-thirds of global incremental consumption by 2021. China, India, Indonesia, Pakistan, Thailand, and Vietnam are among the key growing markets, and in a whole Asia is predicted to take 47.2% share of global beverage market in 2021 [ 153 ].

USA and Europe hold the major share in sterilized food market. However, the Asian market is also expected to show satisfactory growth in the upcoming years. The global sterilization market was valued at $3.1 billion in 2012 and is forecast to reach $4.2 billion by 2017 at a compound annual growth rate of 6.1% [ 154 ].

One of the major revolutionary inventions of human civilization was acquiring the knowledge to preserve foods as it was the precondition to man to settle down in one place and to develop a society. However, increasing shelf lives of food items without compromising original food properties is still critical and challenging. Food is an organic perishable substance, which is susceptible to spoilage due to microbial, chemical, or physical activities. Different traditional techniques, such as drying, chilling, freezing, and fermentation, had been evolved in the past to preserve foods and to maintain their nutrition value and texture. With time and growing demands, preservation techniques have been improved and modernized. Irradiation, high-pressure food preservation, and pulsed electric field effect are the latest innovations used to increase shelf life of foods. Different chemical reagents have also been introduced as food additives and preservatives. However, there are growing concerns of using chemical additives and preservatives in food items because of possible health hazards.

To meet the growing demand of consumers, food preservation and processing sector has been expanding in a rapid manner. To ensure food safety and long shelf life of foods, it is important to understand food spoilage mechanisms and food preservation techniques. This review has compiled and discussed different food categories, different food spoilage mechanisms, and mechanisms and applications of traditional and advanced food preservation techniques. This article will be useful for the professionals and researchers working on food processing and food safety to develop effective and integrated methods to preserve foods.

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Authors contributions

SKA and MMU carried out a major part of the literature review and drafted the manuscript. RR and SMRI carried out literature review for selected sections and helped to revise the manuscript. MSK conceived the study, supervised the research project, coauthored and supervised manuscript preparation, and helped to finalize the manuscript. All authors read and approved the final manuscript.

Acknowledgements

This research was supported by BCEF Academic Research Fund and CASR Research Fund, BUET. The research and manuscript are free of conflict of interest.

Sadat Kamal Amit and Md. Mezbah Uddin are equally first author.

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Sadat Kamal Amit and Md. Mezbah Uddin contributed equally to this work

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Sadat Kamal Amit, Md. Mezbah Uddin, Rizwanur Rahman, S. M. Rezwanul Islam & Mohidus Samad Khan

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Amit, S.K., Uddin, M.M., Rahman, R. et al. A review on mechanisms and commercial aspects of food preservation and processing. Agric & Food Secur 6 , 51 (2017). https://doi.org/10.1186/s40066-017-0130-8

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ENCYCLOPEDIC ENTRY

Preservation.

Preservation and conservation are both processes that protect the environment, but their approaches are somewhat different. The goal of preservation is to protect the environment from the harmful effects of human activity.

Biology, Ecology, Earth Science, Climatology, Geography, Human Geography

Buffalo and Crane

Wildlife and land preservation efforts help protect diverse wildlife populations such as this Asian water buffalo (Bubalus bubalis) and grey heron (Ardea cinrea) in Yala National Park, Sri Lanka.

Photograph by Cezary Wojtkowski

The words preservation and conservation are often used interchangeably, but the two concepts are quite different. Conservation protects the environment through the responsible use of natural resources. Preservation protects the environment from harmful human activities. For example, conserving a forest typically involves sustainable logging practices to minimize deforestation. Preservation would involve setting aside part or even all of the forest from human development.

Why is preservation necessary? In 1800, the world’s population was one billion people. Today it is over seven billion—and continues to rise. An increase in people means greater demand for water, food, lumber , and other resources that come from natural environments. Increasing demand can drive people to exploit resources, even in regions well protected by preservation laws. Dzanga-Ndoki National Park is a protected region in Central Africa. Yet in 2013, poachers entered the region and killed 26 elephants for their tusks.

Successful preservation efforts often rely on shared responsibility between communities, organizations, and governments. In China, preserving the giant panda’s ( Ailuropoda melanoleuca ) habitat over the last decade has increased the panda population. As a result, in 2016 the panda was removed from the endangered species list and reclassified as “vulnerable,” which is a step in the right direction.

Wetlands are also hotspots for preservation. Wetlands improve water quality and minimize flooding and erosion. The Okavango Delta is the largest freshwater wetland in Africa. In 2015, National Geographic Explorer Steve Boyes launched the Okavango Wilderness Project to preserve a region that provides over 95 percent of the water to this delta.

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• Traditional vs Modern Techniques of Food Preservation: Understanding the Pros and Cons

Traditional vs Modern Techniques of Food Preservation: Understanding the Pros and Cons

Food preservation is an age-old practice aimed at preventing the growth of harmful microorganisms and the spoilage of food. Throughout the years, various techniques of food preservation have been developed, ranging from traditional techniques to modern methods. In this article, we’ll take a closer look at the differences between traditional and modern food preservation methods, exploring their pros and cons and how they impact the taste, nutrition, and safety of food.

Traditional Techniques of Food Preservation

Traditional food preservation techniques are methods that have been passed down from generations and have been used for centuries. These methods include:

• Salting: This method involves preserving food by exposing it to salt, which helps to draw out moisture and inhibit the growth of bacteria. This is a common method of preserving meat and fish.
• Drying : Drying is another ancient method of food preservation that involves removing moisture from food by exposing it to sun, wind, or heat. This method is commonly used for fruits, vegetables, and grains.
• Smoking: Smoking involves exposing food to smoke from burning wood or other materials. The smoke imparts flavor and helps to preserve the food by inhibiting the growth of bacteria and other harmful microorganisms.
• Pickling: Pickling involves preserving food in vinegar or a salt-water solution. The acidic environment created by the vinegar helps to preserve the food and also adds flavor.
• Fermentation: Fermentation is a traditional food preservation method that involves exposing food to bacteria, yeast, or other microorganisms. The microorganisms consume the sugars in the food and produce lactic acid, which helps to preserve the food and also imparts a tangy flavor.

Pros of Traditional Food Preservation Techniques

• Tasty: Traditional food preservation methods often add unique and delicious flavors to food, making it taste even better.
• Cost-Effective: Traditional food preservation methods are often less expensive than modern methods, as they make use of readily available materials like salt, vinegar, and sunlight.
• No Chemicals: Traditional food preservation methods do not involve the use of chemicals, which is a big advantage for those who are looking for chemical-free food options.

Cons of Traditional Food Preservation Techniques

• Incomplete Preservation: Traditional methods may not be as effective at preserving food as modern methods, as they do not provide complete protection against the growth of harmful bacteria.
• Time-Consuming: Traditional food preservation methods can be time-consuming, as they often involve lengthy preparation and waiting times.
• Nutritional Loss: Traditional food preservation methods can lead to some loss of nutrients, as the food is exposed to salt, vinegar, and heat, which can break down certain vitamins and minerals.

Modern Food Preservation Techniques

Modern food preservation techniques are methods that have been developed using scientific knowledge and technology. These methods include:

• Canning: Canning involves sealing food in airtight containers, typically made of glass or metal, and then heating the containers to kill off harmful bacteria and microorganisms.
• Freezing: Freezing is a popular modern food preservation method that involves storing food at extremely low temperatures, typically below 0°F. This helps to slow down the growth of bacteria and other harmful microorganisms, allowing food to be stored for extended periods of time.
• Irradiation: Irradiation is a newer method of food preservation that involves exposing food to ionizing radiation. This helps to kill off harmful bacteria and microorganisms, allowing food to be stored for longer periods of time.
• Vacuum Packaging: Vacuum packaging involves removing the air from food packaging, creating a vacuum-sealed environment that helps to slow down the growth of bacteria and other harmful microorganisms.

Pros of Modern Food Preservation Techniques

• Effective Preservation: Modern food preservation methods are much more effective at preserving food than traditional methods, as they provide complete protection against the growth of harmful bacteria and other microorganisms.
• Convenient: Modern food preservation methods are often more convenient than traditional methods, as they do not require lengthy preparation or waiting times.
• Longer Shelf Life: Modern food preservation methods allow food to be stored for much longer periods of time, without losing its quality and taste.

Cons of Modern Food Preservation Techniques

• Expensive: Modern food preservation methods can be more expensive than traditional methods, as they often involve the use of specialized equipment and technology.
• Chemical Use: Some modern food preservation methods involve the use of chemicals, which may not be ideal for those who are looking for chemical-free food options.
• Loss of Flavor: Modern food preservation methods can sometimes lead to a loss of flavor, as the food is not exposed to the natural processes that impart flavor, like smoking and fermentation.

Final Thoughts

Both traditional and modern food preservation methods have their pros and cons, and the best method for preserving food will depend on individual needs and preferences. Traditional methods provide unique and delicious flavors, while modern methods provide effective preservation and longer shelf life. Ultimately, the decision on which method to use will depend on the importance of factors such as taste, nutrition, cost, and convenience.

Keywords: Food preservation, traditional techniques, modern techniques, salting, drying, smoking, pickling, fermentation, canning, freezing, irradiation, vacuum packaging, techniques of food preservation, list of techniques of food preservation, techniques of food preservation list, types of techniques of food preservation, list of types of techniques of food preservation, types of food preservation, traditional types of food preservation, modern types of food preservation, list of modern types of food preservation, list of traditional types of food preservation

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• Biology Article
• Food Preservation Methods Food Poisoning

Food Preservation Methods - Food Poisoning

Food is a source of energy for all of us. Unhealthy or spoiled food is the major cause of diseases in humans. This is known as food poisoning. To prevent this the food needs to be preserved in a variety of ways. Read on to explore what is food preservation and different methods of food preservation.

Also Read:  Food Processing

Food Preservation Definition

“Food preservation is the technique to prevent food spoilage, food poisoning, and microbial contamination in food.”

What is Food Preservation?

Food preservation is one of the methods to protect food from unwanted microbial growth. After the food is produced, we store and protect by covering the rice and curry with lids to keep away flies and other insects. By this, we are protecting it from any infection caused by them. This is a short-term condition. Food preservation, on the other hand, is done to preserve food for a longer time.

Objectives of Food Preservation

Following are the important objectives of food preservation:

• To prevent microbial contamination.
• To kill pathogens.
• To minimise food spoilage and food poisoning.

Food Preservation Methods

Food preservation started long back in ancient times. Cooling, freezing, fermentation, sun-drying, etc., are few age-old food preservation techniques. With the advent of technology, modern methods of food preservation were developed. Chemicals and other natural substances were used for preservation. These substances are known as preservatives. Let us discuss some of the methods of preservation in detail.

Methods of Food Preservation

Chemical Method

Salt and edible oils are two main preservatives which are used since ages to prevent microbial growth. This is why we add extra oil to pickles. Preservation by salt is known as salting. Salting helps to preserve fruits for a long term. Meats and fishes can also be preserved by salting.

Other synthetic preservatives include vinegar, sodium benzoate, sodium metabisulphite, etc.

Sugar is another common preservative used in jams and jellies. Sugar is a good moisture absorbent. By reducing moisture content, it restrains the microbial growth.

Heat and Cold Methods

Boiling and refrigeration prevent around 70 percent of microbial growth. Boiling kills the microorganisms that cannot tolerate extreme temperatures. Thus, it helps in food preservation.

Refrigerators have very low temperatures. Since microbes do not get optimum temperature they need for growth, their growth is inhibited. Pasteurization developed by Louis Pasteur is used until today to preserve milk.

Smoking prevents dehydration in fish and meat and thus prevents spoilage. The wood smoke contains a large number of anti-microbial compounds that slow the rancidification of animal fats.

The food contents are sealed in an airtight container at high temperatures. Meat, fish, fruits are preserved by canning.

Sterilization

This method is carried out to remove microbes from food. For eg., milk sterilization at 100°C kills the microbes.

Dehydration

It is the process of removal of water from food. It is the simplest method and prevents food spoilage by removing water.

Lyophilization

This is the process of freezing and dehydration of the frozen product under vacuum.

This method is also known as cold sterilization. The UV rays, X rays, gamma rays kill all the unwanted microbes present in food.

Also Read: Food Poisoning

The principle behind all these methods is either to reduce the temperature conditions required for microbial growth or to evaporate the water content.

To learn more about what is food preservation, its definition and food preservation methods, keep visiting BYJU’S website or download BYJU’S app for further reference.

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Nice work Good 🙂🙂🙂🙂

I want to ask that can you give some methods definition like pickling, canning, bottling, deep freezing, drying, refrigerating only this much definition

Thank you for your interest. We will update topics for that very soon.

What is fermentation???????????????????

Fermentation is a process by which molecules such as glucose are broken down anaerobically to produce alcohol and acid. Read more at https://byjus.com/biology/fermentation-anaerobic-respiration/

Explain 5 methods of food preservation.

What is nitrogen fixation?

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The Inclusive Historian's Handbook

Historic Preservation

Historic preservation is often linked, hand in hand, with ideas of placemaking, where preservationists embed their work in a neighborhood, community, or landscape to highlight what makes that place unique and preserve its character. [i]  In doing this work, preservationists make evaluations about a place’s beauty, integrity, and significance. In the United States, the criteria on which they base these determinations come largely from the standards listed in the National Register of Historic Places’ nomination process. As the work of historic preservation has evolved in recent years, however, many practitioners have begun to push back against these limited criteria. More people are looking to tell the stories of underrepresented communities, document and protect vernacular architecture, preserve sites of the recent past, and promote the protection of intangible heritage.

More than fifty years after the passage of the National Historic Preservation Act in the United States, more individuals and institutions are recognizing the need to go beyond preserving big houses and places that match traditional standards of architectural beauty. This call to action is pushing the historic preservation movement to embrace inclusive practice—one that not only focuses on the protection of buildings, but also on documenting and sharing the richly varied stories that define places. The goal is to forge a people-centered preservation movement that is inclusive, community driven, and intersectional in nature. [ii]

Early History of the Preservation Movement 

There are two events that are often cited as critical to the founding of historic preservation as a movement in the United States. The first is the story of Ann Pamela Cunningham, founder of the Mount Vernon Ladies Association, who rallied women from across the United States in the 1850s to advocate for the protection and preservation of George Washington’s home. The first call of its kind, it opened conversations about preserving and protecting key sites critical to the history of the United States. The second event, taking place just over a century later, was the loss of the magnificent Pennsylvania Railroad Station in New York City. The destruction of this structure spurred those working in the nascent field to come together, leading eventually to the passage of the 1966  National Historic Preservation Act  (NHPA). The NHPA, which included the creation of the  Advisory Council on Historic Preservation  and the  National Register of Historic Places , enabled the development of a regulatory process for the protection of historic places. [iii]

Much of the NHPA’s framework came from a report called  With Heritage So Rich .  Developed by the Special Committee on Historic Preservation within the U.S. Conference of Mayors, this report ended with a series of recommendations and this statement: “In sum, if we wish to have a future with greater meaning, we must concern ourselves not only with the historic highlights, but we must be concerned with the total heritage of the nation and all that is worth preserving from our past as a living part of the present.” [iv] Although the preservation movement has struggled to realize this ambitious vision, contemporary practitioners have embraced a renewed call for broader and more diverse understandings of preservation and its role in society. Significant challenges exist, however, for those who seek to reorient preservation practice.

Focusing on People

A key element of inclusive preservation practice is the need to shift from an exclusive focus on the  places  being protected to the  people  who have lived and continue to live in those places. We must also pay more attention to the impacts of preservation projects on neighborhoods and communities.

In an anthology marking the 50th anniversary of the NHPA, former National Trust for Historic Preservation Chief Preservation Officer David J. Brown stated: “To build a movement for all Americans, we must recognize that preservation takes many more forms . . . than the ones associated with our work today. Frankly we need tools that give every person a voice in determining what is worth preserving in their community.” [v]  In the same article, Brown emphasizes the need to move away from a one-size-fits-all approach toward a more nuanced understanding of how to work collaboratively with communities to determine what places to protect. [vi]

Leading up to the anniversary of the NHPA, the National Trust for Historic Preservation held a series of listening sessions across the country. These sessions included individuals who were active in the preservation profession as well as voices from outside the field. These conversations coalesced into a vision for the future of preservation.  The report ,  Preservation for People , centers around three different principles:

• A people-centered preservation movement hears, understands, and honors the full diversity of the ever-evolving American story.
• A people-centered preservation movement creates and nurtures more equitable, healthy, resilient, vibrant, and sustainable communities.
• A people-centered preservation movement collaborates with new and existing partners to address fundamental social issues and make the world better.

Preservation for People  seeks to lay out strategies and tactics to make preservation more democratic, inclusive, and equitable. Essential to achieving these goals is building a more inclusive profession. Historically, preservation has been seen as an elitist practice, and while the demographics of the field are slowly shifting, there are still significant barriers to entry.

It is critical to demonstrate to young people that preservation is something that is relevant to their lives. During the 2015  PastForward  Diversity Summit Jose Antonio Tijerino, president and CEO of the Hispanic Heritage Foundation, stated that “the first step is reaching out. And also making it relevant. How is it relevant to a young black man? Woman? A young Latino? Young Asian? Young LGBT? To be able to feel connected to what your mission is . . .” [vii]

Some organizations have made telling underrepresented stories and protecting places that are sharing these narratives central to their work. For example, Asian Pacific Americans in Historic Preservation and Latinos in Heritage Conservation (LHC) have worked to support a network of individuals who are engaged in these types of projects. Sarah Zenaida Gould of LHC says that “We envision this network as one that equally welcomes professional preservationists  and  community preservationists. For we all have knowledge, ideas, experiences, and strategies to share.” [viii]

In summarizing the 2015 Diversity Summit which took place at PastForward, Stephanie K. Meeks, then CEO and President of the National Trust for Historic Preservation, stated:

Over the course of the discussion, common themes emerged. All of the panelists agreed that recognizing and honoring diverse stories was key to understanding our present political debates and to building a more inclusive and allied future. All felt that, while we have made important strides as a movement, we still have a lot of work to do to get this right. All believed that forging stronger partnerships with and across diverse groups was essential for continued success. And all emphasized the wisdom of today’s broader vision of preservation, in which we seek to save the modest and even ordinary places where history happened. [ix]

Re-thinking the Preservation of Places

In recent years, the National Trust for Historic Preservation has begun to look more closely at the impacts of preservation in cities through an initiative called ReUrbanism. Fundamental to ReUrbanism is the idea that building reuse encourages economic growth and stimulates vibrant communities. Through a variety of studies, the National Trust has found that mixed use neighborhoods are often more sustainable than those communities with a single building stock. [x]  Many of the  principles of ReUrbanism  look toward creating equity in neighborhood development and planning, and derive from a broader conversation with the field about preservation planning in urban areas. In a piece for the  Forum Journal’s issue on ReUrbanism , Justin Garrett Moore describes the need to change preservation and planning processes. The example he uses is a new community playbook in New York City. This  Neighborhood Planning Playbook

includes tools designed to reveal the complexities of a neighborhood and provide a framework for comprehension, communication, education, and exchange with community residents and stakeholders. The playbook aims to help the city better study, develop, and implement plans for neighborhood change—and, most importantly, build public engagement and communication into all stages of the work. [xi]

Community engagement is a key piece of ReUrbanism. There is an evolving understanding that preservationists need to shift from an authority-based model to one that works in tandem with those who will be most impacted by preservation efforts.

Additionally, it is important to recognize that the protection of place also involves a full engagement in issues surrounding climate change. In her series on  America’s Eroding Edges ,  Victoria Herrmann , a National Geographic Explorer and president and managing director of the Arctic Institute, examines the role flooding, coastal erosion, melting permafrost, and other climate impacts have not just on buildings and tangible heritage, but also on traditional cultural practices and entire communities. While it is paramount that we develop a robust set of strategies to adapt historic resources to climate impacts, these efforts must go hand in hand with conversations about economic and cultural equity and resilience.

In her 2018 TrustLive talk at PastForward, Herrmann discussed how in all of her conversations with communities impacted by climate change, the one consistent factor is that “climate change is the looming reality of losing the places and histories that make us who we are.” She continues to say that “climate change is not race, gender, or income neutral. Low-income communities, communities of color, and women are disproportionally affected by climate impacts. From centuries of discriminatory, social, and environmental policies, these communities have not been able to create the resources they need to prepare for and adapt to climate disasters.” With this in mind, inclusive preservation practice must include a recognition of climate impacts on communities; it is through dialogue and partnerships with organizations such as the Union of Concerned Scientists, 100 Resilient Cities, US ICOMOS, and the Association for Preservation Technology that the practice can move forward.

It is clear that many of the places currently being preserved only protect a fraction of historical narratives. Clement Price, who was a former Trustee of the National Trust and a Vice Chair of the Advisory Council on Historic Preservation, stated that broadening the spaces being preserved “connects very ordinary Americans with their personal histories, and in turn these histories connect with the larger narrative of making a more perfect and yet complicated union.” [xii]  Examples of such places exist across the United States and, in recent years, some have become the focus of preservation efforts.

Two important examples are Tule Lake, a Japanese internment camp, and  Rio Vista Farm in Texas , an agricultural site where migrant laborers from Mexico toiled. One site is evidence of the challenges to U.S. democracy that arose when segments of the U.S. population were unconstitutionally incarcerated due to racist fears and wartime hysteria; the other is a place that demonstrates how migrant workers from Mexico filled critical gaps in the U.S. agricultural labor system. In both cases, we find pieces of U.S. history that are often overlooked and, in doing so, begin to recognize the layers of experience and history that can be encountered in these places.

Speaking about sites such as Tule Lake, Cathlin Goulding writes, “Though the euphemisms for these places range, they all have in common a political climate of fear, suspicion, and hysteria and a system of governance wherein power is ultimately rooted in the ability to decide who can and does belong.” [xiii]

Inclusive Storytelling

The final pivot for preservation as an inclusive practice is something that runs parallel to work within both public history and museums: storytelling. In some ways this term feels like the latest buzzword across disciplines; nevertheless, it is an important piece of the broader mission of preservation as we strive to tell fuller and richer stories. In order to know what places to protect, we have to listen to the people to whom these stories belong; in doing so, it is important to recognize that these stories cannot be told using the same methods and practices as before. An inclusive preservation practice recognizes that preservation is not just about buildings and structures but also  intangible heritage , which is often only available through conversations with community members.

Consider the work of the San Antonio Office of Historic Preservation, which uses a process called culture mapping to make connections to place and document change over time. Claudia Guerra, from San Antonio’s Office of Historic Preservation, describes the process where recorded narratives are paired with hand-drawn maps from community storytellers. She emphasizes the need to protect the intangible: “Safeguarding and preserving our heritage is what preservationists do, but preservation is about more than just protection—it is inherently about sharing.” [xiv]  In her essay, she emphasizes a variety of tools and lessons critical to working with communities: “Listen more than you speak.” “Be prepared for unusual places to be documented.” And, “be aware and sensitive to the fact that similar cultural communities that share some traits may nevertheless differ widely in [their] thinking.”

In a sense, the importance of expanding preservation’s scope is to further build connections among people, places, and the past. In an  interview  for the  Preservation Leadership Forum , Angelo Baca, filmmaker and cultural resources director for the Utah Diné Bikéyah, stated that “stories are very important because they hold knowledge. And it is important for us to understand that even the oral traditions, the legends, the myths, and all these things that talk about the time before what we understand now are actually . . . a resource.” For many Native communities, the importance of place is centered in both the tangible and the intangible. The identity of many of these communities is rooted not only in physical places but also the traditional knowledge embedded within those places.

Lisa Yun Lee, director of the National Public Housing Museum, says it best when she states “Our commitment to preservation and interpretation must always include a commitment not only to telling a narrative or presenting a counter-narrative but also to meaningfully empowering people to change the narrative.” [xv]

An Inclusive Preservation Practice

In the edited collection  Bending the Future , Gail Dubrow, professor at the University of Minnesota, writes:

My vision and hope…is that these relatively new advocacy groups and constituencies move from the margins to the center of the preservation movement, bring their independent identity-based preservation interests into more effective alliances that bridge the divides of race, class, gender, and sexuality. While identity based politics have resulted in a more inclusive agenda for what we preserve, the democratic future of how we preserve depends on bringing their experiences, insights, and perspectives to bear on redefining the scope, policies, practices, and priorities of the preservation movement as a whole. [xvi]

Building inclusive preservation practices requires acknowledging the stories, places, and needs of all communities. Tried-and-true preservation tools need to be used in tandem with other methods and practices. Collaboration and partnership are essential to protecting places in a fair and equitable way.

Historic preservation can be a force for good rather than a tool of elitist forces, but in order to make it so, many of the field’s practices need to shift. This reorientation is essential because, as Tom Mayes, author of  Why Old Places Matter , writes, “The old places of people’s lives are deeply important—more important than is generally recognized—because these neighborhoods, churches, temples, old houses, stone-walled fields, landmark trees, and courthouses contribute to people’s well-being, from that sense of identity and belonging, to the awe inspired by beauty, to the drive to build and sustain a greener and more equitable world.” [xvii]

[i] A growing conversation in the art community is centered around the vocabulary of placemaking. During a 2018 PastForward session Lauren Hood  from Deep Dive Detroit talked about the concept of  place-keeping  where instead of coming into a neighborhood and rebuilding from the ground up, preservationists and art organizers work to support and sustain the cultural practices that already exist. In order to have an inclusive preservation practice, language is an important element to focus on. See also Erica Ciccarone, “ Nashville Artist’s Aim for Place-keeping More Than Placemaking ,” Burnaway , September 17, 2017.

[ii] Coined in 1989 by law professor Kimberlé Crenshaw,  intersectionality  is a term that examines the overlapping issues of discrimination within specific identities. That is, where stories of discrimination for black women are often connected to discrimination bias based on their gender and race. For the purposes of this essay, intersectionality uses that central definition as a means of storytelling, in which preservationists and historians tell the full history of the American past through the lens of overlapping identities.

[iii] Max Page and Marla Miller, “Introduction,” in  Bending the Future: Fifty Ideas for the Next Fifty Years of Historic Preservation in the United States,  eds. Max Page and Marla Miller (Amherst, MA: University of Massachusetts Press, 2016), 2.

[iv] Byrd Wood, ed.  With Heritage So Rich  (Washington D.C.: National Trust for Historic Preservation, 1999), 194.

[v] David Brown, “A Preservation Movement for All Americans” in  Bending the Future: Fifty Ideas for the Next Fifty Years of Historic Preservation in the United States,  eds. Max Page and Marla Miller (Amherst, MA: University of Massachusetts Press, 2016), 59.

[vi] Brown, “A Preservation Movement for All Americans,” 60.

[vii] Stephanie Meeks, “Introduction: Our Future Is In Diversity,”  Forum Journal: The Full Spectrum of History: Prioritizing Diversity and Inclusion in Preservation 30, no. 4 (Summer 2016): 9. There are a two significant programs that work to engage youth in preservation projects. The National Trust’s  HOPE Crew  focuses on training young people and veterans in historic trades. Another program,  HistoriCorps , was inspired by the Depression-era Civilian Conservation Corps to bring volunteers together to work on preservation projects. Both programs provide avenues of engagement outside of professional university training.

[viii] Sarah Zenaida Gould, “Latinos in Heritage Conservation,” in  Bending the Future: Fifty Ideas for the Next Fifty Years of Historic Preservation in the United States,  eds. Max Page and Marla Miller (Amherst, MA: University of Massachusetts Press, 2016), 89.

[ix] Meeks, 6.

[x] More detail on these ideas can be found in the National Trust for Historic Preservation research reports Older, Smaller, Better : Measuring how the character of buildings and blocks influences urban vitality and Untapped Potential: Strategies for Revitalization and Reuse .

[xi] Justin Garrett Moore, “Making A Difference: Reshaping the Past, Present, and Future Toward Greater Equity,”  Forum Journal: Reurbanism: Past Meets Future in American Cities  31, no. 4 (2018): 23-24.

[xii] Clement Alexander Price, “The Path to Big Mama’s House: Historic Preservation, Memory and African-American History,”  Forum Journal: Imagining a More Inclusive Preservation Movement  28, no. 3 (2014): 27.

[xiii] Cathlin Goulding, “Tule Lake: Learning from Places of Exception in a Climate of Fear,”  Forum Journal: Preserving Difficult Histories  31, no. 3 (Spring 2017): 50.

[xiv] Claudia Guerra, “Culture Mapping: Engaging Community in Historic Preservation,” Forum Journal: The Full Spectrum of History: Prioritizing Diversity and Inclusion in Preservation 30, no. 4 (Summer 2016): 30.

[xv] Lisa Yun Lee, “The Stories We Collect: Promoting Housing as a Human Right at the National Public Housing Museum,”  Forum Journal: Preserving Difficult Histories  31, no. 3 (Spring 2017): 17.

[xvi] Gail Dubrow, “From Minority to Majority,” in  Bending the Future: Fifty Ideas for the Next Fifty Years of Historic Preservation in the United States,  eds. Max Page and Marla Miller (Amherst, MA:  University of Massachusetts Press, 2016), 74.

[xvii] Thompson M. Mayes,  Why Old Places Matter: How Historic Places Affect Our Identity and Well-Being  (New York: Rowman & Littlefield Publishers/AASLH, 2018).

Suggested Readings

Baca, Alex. “Places Journal Reading Lists: Reading Cities.”  Places Journal . https://placesjournal.org/reading-list/reading-cities/ .

Herrmann, Victoria. “Blog Series: America’s Eroding Edges.” October 1, 2018,  https://forum.savingplaces.org/blogs/forum-online/2018/10/01/blog-series-americas-eroding-edges . More stories at  www.erodingedges.com .

Mayes, Thompson M.  Why Old Places Matter: How Historic Places Affect Our Identity and Well-Being .  New York: Rowman & Littlefield Publishers/AASLH, 2018). Blog Series here:  https://forum.savingplaces.org/blogs/forum-online/2016/03/30/blog-series-why-do-old-places-matter .

Meeks, Stephanie K. “Presenting ‘Preservation for People: A Vision for the Future.’”  Preservation Leadership Forum . May, 18, 2017,  https://forum.savingplaces.org/blogs/stephanie-k-meeks/2017/05/18/presenting-preservation-for-people-a-vision-for-the-future .

National Council on Public History. “Special Issue: Conversations in Critical Cultural Heritage”  The Public Historian 41, no. 1 (February 2019).

National Council on Public History. “National Historic Preservation Act Commemoration Series”  History@Work blog,  https://ncph.org/history-at-work/tag/national-historic-preservation-act-commemoration/ .

National Park Service. “Theme Studies.” Accessed February 16, 2019,  https://www.nps.gov/subjects/nationalhistoriclandmarks/recent-theme-studies.htm .

• Finding A Path Forward: Asian American Pacific Islander National Historic Landmark Theme Study. 2018.
• LGBTQ America: A Theme Study of Lesbian, Gay, Transgender, and Queer History. 2016.
• American Latino Heritage. 2013.

Page, Max, and Marla Miller, eds.  Bending the Future: Fifty Ideas for the Next Fifty Years of Historic Preservation in the United States .  Amherst, MA: University of Massachusetts Press, 2016.

Preservation Leadership Forum.  Forum Journal: The Full Spectrum of History: Prioritizing Diversity and Inclusion in Preservation 30, no. 4 (Summer 2016).

Preservation Leadership Forum.  Forum Journal: Preserving Difficult Histories   31, no. 3 (Spring 2017).

Preservation Leadership Forum.  Forum Journal: “Every Story Told”: Centering Women’s History 32, No. 2. Behind a Firewall Until 2020. Available on Project Muse.

Preservation Leadership Forum.  Forum Journal: Imagining a More Inclusive Preservation Movement  28, no. 3 (2014).

Smithsonian Asian Pacific American Center. “Culture Lab Playbook.” Accessed February 16, 2019,  https://smithsonianapa.org/culturelab/ .

UNESCO. “About Intangible Heritage.” Accessed February 16, 2019,  https://ich.unesco.org/en/what-is-intangible-heritage-00003 .

US/ICOMOS. “With a World of Heritage So Rich.”  US/ICOMOS Organization Website . Accessed February 16, 2019  http://www.usicomos.org/about/wwhsr/ .

Valadares, Desiree. “Places Journal Reading Lists: Race, Space, and the Law.”  Places Journal.  https://placesjournal.org/reading-list/race-space-and-the-law/ .

Various Authors. “Blog Series: When Does Preservation Become Social Justice.”  Preservation Leadership Forum . July 26, 2017.  https://forum.savingplaces.org/blogs/forum-online/2017/07/26/blog-series-when-does-preservation-become-social-justice .

Various Authors. “Blog Series: Women’s History and Historic Preservation.”  Preservation Leadership Forum .  September 13, 2017.  https://forum.savingplaces.org/blogs/forum-online/2017/09/13/blog-series-womens-history-and-historic-preservation .

~  Priya Chhaya  is a public historian and the associate director of publications and programs at the National Trust for Historic Preservation. You can contact her through her website at  www.priyachhaya.com .

From the President

Preserving the Past

James J. Sheehan | Apr 1, 2005

It is hard for us to imagine that the inhabitants of Rome once quarried the ruins of ancient temples for stones to build their houses or that German bureaucrats in the early 19th century used books taken from monastic libraries to pave their roads. We always find it painful to learn that some historical treasure has been destroyed, either by war, like the great abbey at Montecassino, or by political vandalism, like the contents of Baghdad's museums, or by accident, like the Anna Amalia library in Weimar. The residues of the past, we recognize, are both fragile and precious, things that need to be protected and preserved.

This recognition of the past's vulnerability is an important part of history's cultural origins and a significant source of its endless fascination. "The poetry of history," wrote G. M. Trevelyan, "lies in the quasi-miraculous fact that once, on this earth, on this familiar spot of ground, walked other men and women, as actual as we are today, thinking their own thoughts, swayed by their own passions, but now all gone, one generation vanishing after another, gone as utterly as we ourselves shall shortly be gone like ghosts at cock-crow." The great Polish poet, Czeslaw Milosz (who knew a lot about the meaning of loss), once said that "only an awareness of the dangers menacing what we love allows us to sense the dimension of time and to feel in everything we see and touch the presence of past generations."

Although a concern for the past's vulnerability has been around for centuries, it has recently been intensified by the increasingly destructive power of change that we sense all around us. Everywhere we turn we find signs that large pieces of our world are being torn down, paved over, violently extinguished. According to one estimate more than 50 acres of the earth's forests are destroyed every minute; of the 242,000 plant species surveyed in 1997, some 33,000 are supposed to be at risk; among the 6,800 distinct languages now spoken throughout the world, 400 are restricted to a handful of speakers and will soon disappear, while another 3,000 are in danger of extinction. We face, in other words, a future in which our planet's rich natural and cultural variety will steadily decline, leaving us diminished in ways difficult to measure and understand.

Because we feel so much is slipping away from us, our society devotes an enormous amount of time and effort to saving what it can from the wreckage. New museums open every day, steadily expanding their scope from art and antiquities to a bewildering variety of human artifacts and natural environments. (Earlier this year, a Museum of the American Cocktail was founded—where else?—in New Orleans.) In his informative review essay on museums in the February 2005 AHR, Randolph Starn reports that there are 25,000 accredited museums in the world, 8,000 in the United States; the total number of smaller institutions is several times larger. The museum has become our modern society's most significant cultural institution, a source of meaning, legitimacy, and, perhaps above all, of reassurance that some pieces of the past will be preserved.

There is, of course, a paradox at the heart of preservation. To protect things from the damaging forces of history, it is necessary to remove them from harm's way, which often means stripping them of their original meaning and purpose. Joseph Levenson nicely captured this paradox with the following example taken from a guidebook describing the tomb of the great Chinese patriot, Yueh Fei:

Before the tomb kneel the figures of the traitor Ch'in Kuei, his wicked wife, his accomplice Mochi Hsueh, and Chang Chun who deserted Yueh Fei at the critical moment. It was the tradition for tourists to throw stones and other objects at these figures to show their contempt for their treachery. But nowadays the practice has been discontinued owing to the need for preserving the figures which are of historical value.

— Quoted by Frederic Wakeman in his introduction to Levenson's Revolution and Cosmopolitanism (Berkeley, 1971), xiv.

Who, Levenson wants us to wonder, understood the historical value of these statues better, those who cared enough to throw stones at them or those who turned them into objects of disinterested admiration?

As old as the museum is a persistent uneasiness about the enterprise of preservation. In the early 20th century, avant-garde artists fantasized about "kidnapping" the Mona Lisa or even burning down the Louvre; museums, libraries, and archives often appear in novels and films as emblems of sterility. In his frequently—perhaps too frequently—quoted essay, "Valéry Proust Museum," Theodor Adorno called museums "the family sepulchers of works of art," and drew attention to the linguistic similarity between museum and mausoleum. The literature by and about museum professionals is filled with self-critical questions about the institution's place in contemporary culture and society.

The museum's critics usually underestimate the amount of energy and erudition required to identify, classify, and preserve the past. Nor do these critics tell us what the alternatives to museums might be. Are we really prepared to leave the sculpture at Yueh Fei's tomb to the mercy of an ever-growing number of stone-throwing visitors? And what about the great statues of the Buddha at Bamiyan in Afghanistan, which were blown up by the Taliban, who thereby expressed an intense but terminal regard for their historical significance?

As the custodians and protectors of the past, museum professionals deserve our respect and support. "Museums and history are close kin," Starn eloquently argued in his AHR essay, but they tend to remain in their own separate institutional spheres. It is time we began to pay more attention to one another: perhaps, in addition to reviewing films, the AHR should review important museum collections and special exhibitions, thereby recognizing the vital role they play in both the preservation and presentation of the past.

Not long ago I heard a lecture about the International Maize and Wheat Improvement Center, located near Mexico City, where scientists have created a genebank that preserves an immense collection of seeds from wild and domesticated cereal plants. Their work is part of a larger scientific project to improve the yields of crops that nourish so many people throughout the world, but I was struck by how this genebank was an apt metaphor for what many historians do when we preserve residues of the past, never knowing when we might need them to nourish future generations.

— James Sheehan (Stanford Univ.) is president of the AHA.

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Cultural heritage: 7 successes of UNESCO’s preservation work

The power of preserving cultural heritage to build a better world

Why do we go to great lengths to preserve culture and make it bloom? Culture is a resource for the identity and cohesion of communities. In today’s interconnected world, it is also one of our most powerful resources to transform societies and renew ideas. It is UNESCO’s role to provide the tools and skills we need to make the most of its ultimate renewable energy.

Historical landmarks, living heritage and natural sites enrich our daily lives in countless ways, whether we experience them directly or through the medium of a connected device. Cultural diversity and creativity are natural drivers of innovation. In many ways, artists, creators and performers help us change our perspective on the world and rethink our environment. These are precious assets to respond to current global challenges, from the climate crisis to the COVID-19 pandemic.

The notion of culture has greatly evolved over the last 75 years. UNESCO’s actions over the past decades bear witness to the many ways in which humanity tried to understand how culture can strengthen the sense of who we are – from the awareness of the necessity to protect heritage from destruction at the end of World War II, to the launch of international campaigns to safeguard World Heritage sites and the concept of living and intangible heritage, a focus on creative economy and the need to sustain cultural jobs and livelihoods. Our relationship with culture has deeply evolved over the last century. If we look into the past, we might be better prepared to tackle further changes ahead.

The United States will be participating in an international effort which has captured the imagination and sympathy of people throughout the world. By thus contributing to the preservation of past civilizations, we will strengthen and enrich our own.

Abu Simbel – We do not have to choose between the living and the dead

A few minutes before sunrise, thousands of visitors line up inside the temple of Abu Simbel, holding their breath. They are about to witness a rare phenomenon that has taken place twice a year for the last 3,000 years. Every February and October at 6:29 am, the light of the rising sun pierces through the narrow entrance. The rays penetrate over 70 metres deep across the giant pillared hall up to the inner sanctuary, illuminating the statue of the man who built the temple during the 13th century BC, Pharaoh Ramses II.

Carved out of a rocky hill, the Temple of the Rising Sun had been conceived to show the might of Egypt’s greatest pharaoh to the Nubian people in the Upper Nile. Over time, the great temple and the smaller buildings became covered in sand and lay forgotten for centuries, until their rediscovery in 1813. The supreme example of ancient Egypt’s knowledge of astronomy and the skill of its architects could be admired again.

But just over a century later, the southernmost relics of this ancient human civilization were threatened with underwater oblivion and destruction by the rising waters of the Nile following the construction of the Aswan High Dam. The construction of the Dam was meant to develop agriculture as well as Egyptian independence and economy, and triggered a global debate that has fuelled media front pages and discussions ever since: should we have to choose between the monuments of the past and a thriving economy for the people living today? Why should people care for ancient stones and buildings when so many people need food and emergency assistance?

In the course of an unprecedented safeguarding campaign to save the temples of Egypt, UNESCO demonstrated that humanity does not have to sacrifice the past to thrive in the present – quite the opposite. Monuments of outstanding universal value help us understand who we are and also represent massive opportunities for development. Two millennia after a Greek author and scientist drew the famous list of the world’s seven wonders, the very notion of World Heritage came to life.

The race against time began in 1964 , when experts from 50 nations started working together under the coordination of UNESCO in one of the greatest challenges of archaeological engineering in history. The entire site was carefully cut into large blocks, dismantled, lifted and reassembled in a new location 65 metres higher and 200 metres back from the river, preserving it for future generations.

Today, the four majestic statues that guard the entrance to the great temple stare at the river and the rising sun every day. As they did 3,000 years ago. The success of the international cooperation to save Abu Simbel raised awareness about the fact that all over the world there are places of outstanding universal value. Just like the Nile valley temples, they must be protected from many threats such as armed conflict, deliberate destruction, economic pressure, natural disasters and climate change.

The World Heritage Convention was adopted in 1972 as the most important global instrument to establish this notion, bringing all nations together in the pursuit of the preservation of the World’s Natural and Cultural Heritage. With its 194 signatory Member States, it is today one of the world’s most ratified conventions.

How is a site inscribed on the UNESCO World Heritage List?

For a site to be inscribed on the UNESCO World Heritage List, it must first be nominated by the country where it is located. The nomination is examined by international experts who decide whether the inclusion is justified. Finally, the World Heritage Committee, a body of 21 UNESCO elected Member States, takes a vote.

Venice – Can the safeguard of cultural heritage and global tourism coexist?

Launched only a few years after the Nubian temples initiative, the safeguarding campaign for Venice was a response to various challenges including the rising waters and the explosion of global tourism.

Stepping  outside the railway station early on an autumnal morning, visitors are met with the view of the chilly air colliding with the water, forming a thick, soft blanket of fog over the Grand Canal, the ‘main street’ of Venice. The church of San Simeone Piccolo, with its oversized dome and slender neoclassical columns, and the neighbouring buildings appear to be floating on the water of the lagoon. It’s a sight that has welcomed millions of visitors from all over the world since the heydays of the Serenissima, when the city ruled as one of Europe’s economic superpowers.

Yet, the breath-taking beauty that inspired countless painters, writers and artists over the centuries remains fragile and at risk of being lost forever. Like the Abu Simbel temples, the city’s survival is threatened by rising water levels. The inexorable increase in sea level has caused flooding to become a regular occurrence. Humidity and microorganisms are eating away the long wooden piles that early dwellers drove deep into the muddy ground of the lagoon to build the first foundations of Venice, 1,600 years ago.

After 1966, the year of the worst flooding in Venice’s history, UNESCO and the Italian Government launched a major campaign to save the city. An ambitious project involving giant mobile flood gates was undertaken to temporarily isolate the lagoon from the high tides and protect the lowest areas from flooding. Thirty years later there is unanimous agreement on the successful results both of the technical achievements and international cooperation.

But Venice still needs attentive care, and its continued survival calls for unflagging vigilance. The city remains threatened on several fronts – mass tourism, the potential damage of subsequent urban development and the steady stream of giant cruise ships crushing its brittle foundations.

International mobilization and pressure around the status of Venice led to the Italian Government’s decision in 2021 to ban large ships from the city centre, as a necessary step to protect the environmental, landscape, artistic and cultural integrity of Venice. This decision came a few days after UNESCO announced its intention to inscribe the city on its World Heritage in Danger list. Until a permanent big cruise docking place is identified and developed, liners will be permitted to pull up in Marghera, an industrial suburb of Venice. Such decisions illustrate the great complexity of protecting historic cities and cultural heritage urban centres, which in this particular situation called for tailor-made measures and techniques different from those implemented for the safeguarding of the fabled Egyptian temples.

If every museum in the New World were emptied, if every famous building in the Old World were destroyed and only Venice saved, there would be enough there to fill a full lifetime with delight. Venice, with all its complexity and variety, is in itself the greatest surviving work of art in the world.

Angkor – A successful example of longstanding international cooperation

Deep in the forests of Cambodia, in the Siem Reap Province, the five lotus-flower-shaped towers of majestic Angkor Wat soar towards the sky. When approaching from the main gate, the vast scale of the temple and the precise symmetry of the buildings are awe inspiring. This is the world's largest religious monument.

Angkor Wat was part of a sprawling city as big as London, the heart of an empire that between the 9th and 15th centuries extended from southern Vietnam to Laos, and from the Mekong River to Eastern Myanmar. By around 1500 A.D., the Khmer capital was abandoned, most likely after heavy floods and lengthy droughts. Its temples, buildings and complex irrigation network were swallowed by the surrounding forests and lay hidden until their rediscovery in 1860.

By the early 1990s, the site was under major threat, with many of the temples at high risk of collapse and several sites looted. Conservation work at Angkor had not been possible since the outbreak of the civil war, the rise of the Khmer Rouge regime and the following civil unrest.

Angkor Wat’s inclusion in UNESCO’s World Heritage List in 1992 marked a milestone in the country’s recovery after years of conflict. The UNESCO-backed preservation of the temples aimed to assist in nation-building and national reconciliation. The action of the International Coordinating Committee (link is external) (ICC-Angkor) for the safeguarding and development of this exceptional cultural site is a striking example of international solidarity and testifies to one of UNESCO's most impressive achievements for heritage. Thirty countries and an ad hoc experts group for scientific, restoration and conservation projects were brought together under an innovative approach, closely linking safeguarding operations to sustainable development efforts.

In 25 years, Angkor has thus become a living laboratory demonstrating the potential of sustainable tourism and crafts, with the mobilization of local communities for social cohesion in 112 villages. The gigantic site now supports 700,000 inhabitants and attracts some five million visitors whose flow must be managed each year. The park authorities are carrying out several projects aimed at improving the lives of communities through the implementation of sustainable tourism that respects local sensitivities. The removal from UNESCO’s List of World Heritage in Danger just fourteen years later is a credit to the Cambodian people.

The fact that a project of such magnitude was successfully carried out in a country emerging from more than two decades of conflict in 1992 is a testament to the potential of the World Heritage Convention and the international solidarity led by UNESCO.

Walking through the temple, I saw reminders of the prosperous civilization that built it: hundreds of beautiful figures carved into the walls telling the stories of these ancient people; wide galleries they must have prayed in; long hallways lined with pillars they must have walked down.

No one knows for sure what caused the empire to abandon this temple and the surrounding city, but in the 15th century almost everyone left. Trees grew over the stones. Only Buddhist monks stayed behind to care for — and pray in — the hidden temples.

But that didn’t stop pilgrims and visitors from continuing to journey here to take in these incredible structures. And now, centuries later, I couldn’t be more thankful to count myself as one of these visitors

Mostar – Symbols do matter, in war and peace

It’s the end of July in Bosnia-Herzegovina. Peak summer means an influx of tourists to the cobbled alleys of Mostar. The cosy medieval town has a long, rich history marked by the peaceful coexistence of three communities: Muslim Bosniaks, Orthodox Serbs and Catholic Croats. Once they arrive in town, visitors from all over the world make a beeline for Mostar’s most emblematic monument, the Old Bridge.

A masterpiece of Ottoman architecture, Stari Most – as it’s known locally – is a symbol of the different communities that have existed side-by-side in the area. Since the 16th century, the bridge had brought them together across the Neretva river – until the Bosnian war. The bridge was a symbol of unity between the Bosnian community (Muslim), in the east of the city, and the Croats and Serbs to the west. The bridge of Mostar (of Ottoman, therefore Muslim origin) served as a link between all these communities – as a pedestrian bridge, it had no military or strategic value. Its destruction in 1993 was only meant to force the communities to separate, to deny their mixing with their neighbours. The bridge was in ruins and, with it, the values of peace and understanding this centuries-old structure had embodied.

Five years later, UNESCO coordinated a reconstruction project to rebuild the Old Bridge. Despite the scars of the war that are still visible today on the city walls, the reconstructed bridge has now become a symbol of reconciliation and post-conflict healing.

Today, the crowds jam the street to watch the traditional diving contest from the top of the bridge, a long-held custom resumed once Stari Most was restored to its former glory. Every July, young people of Mostar’s three communities compete with courage by jumping into the river 29 metres below, just like they did before the war.

For over four years after the ceasefire, former enemies worked together to retrieve the stones from the riverbed and rebuild their former symbol of friendship. Reconstructed in 2004 and inscribed on UNESCO’s World Heritage list in 2006, Stari Most today is a bridge between a common past and a common future. It is certainly not enough to rebuild a bridge to restore confidence and rebuild peace in a war-torn society. But it certainly matters to care for the symbols of peace.

I was in my office, working to the sound of mortar fire, when we heard the cries in the street – cries that the bridge had fallen. And what happened then was so impressive that I will never forget it. Everyone came out to see. Grenades and bombs were falling everywhere, but still they came out of their hiding places: young and old, weak and strong, Muslim and Christian, they all came, all crying. Because that bridge was part of our identity. It represented us all.

Timbuktu – When warlords target heritage, peacemakers respond with more heritage

Sitting at the gateway to the Sahara Desert, Timbuktu conjures images of a mythical city at the end of the world, where Arab and African merchants would travel from afar to trade salt, gold, cattle and grain. In the English language, the city in northern Mali has come to represent a place far away. Undaunted, caravans still ply the cross-desert route and come to the city several times a year. They carry rock salt extracted from the northern Sahara, just like their ancestors did for centuries.

In its heyday, during the 16th century, the city had 100,000 inhabitants, as its mosques and holy sites played an essential role in the spread of Islam in Africa. The city became an important centre of learning in Africa and its libraries the repository of at least 700,000 historical manuscripts on art, science and medicine, as well as copies of the Qur’an. These manuscripts, written in ornate calligraphy, bear witness to the richness of African history and intellectual life.

During the conflict of 2012–2013, more than 4,000 of the 40,000 manuscripts kept at the Ahmed Baba Institute were lost. Some were burnt or stolen, while more than 10,000 remained in a critical condition. The inhabitants of Timbuktu helped save their precious heritage by secretly spiriting away more than 300,000 manuscripts to the capital, Bamako. Other texts were sheltered between mud walls or buried. Although protected from immediate destruction, the manuscripts are now preserved in conditions that may not safeguard them for future generations.

To help preserve Timbuktu’s cultural heritage and encourage reconciliation, UNESCO has been supporting the local communities to take part in ancient manuscript conservation projects and ensure their lasting preservation for humanity.

UNESCO has coordinated the work to rebuild the fourteen mausoleums inscribed on the World Heritage List, as well as the Djingareyber and Sidi Yaha mosques, that were deliberately destroyed by armed groups during the conflict.

The reconstruction of Timbuktu’s devastated cultural heritage aimed to foster reconciliation among communities and restore trust and social cohesion. An important aspect of the project was the drive to include the reconstruction of the mausoleums in an overall strategy aimed at revitalizing building traditions and ensuring their continuity, through on-the-job training activities and conservation projects.

To ensure the rebuilt shrines matched the old ones as closely as possible, the reconstruction work was checked against old photos and local elders were consulted. Local workers used traditional methods and local materials, including alhor stone, rice stalks and banco – a mixture of clay and straw.

The destruction of the mausoleums of Timbuktu has been a shock, and a clear turning point revealing the importance taken of culture and heritage in modern conflicts fuelled by violent extremism and fundamentalist ideologies. It has shown how strongly fundamentalists are willing to destroy other Islamic cultures, and any other vision which differs from their own. Similar direct destruction of Islamic, pre-Islamic, Christian or Jewish heritage, has then been seen in Iraq and Syria. The need to restore heritage has become far more than a mere cultural issue – it has become a security issue, and a key component for the resilience and further cohesion of societies torn by conflicts.

At present, the monuments in Timbuktu are living heritage, closely associated with religious rituals and community gatherings. Their shape and form have always evolved over time both with annual cycles (that of the rain and the erosion of the plastering); that of regular maintenance (every three to five years); repairs of structural pathologies, often adding buttresses; and at times more important works, including extensions and raising of the roof structure. How to take that into account while trying to guide and assist the local people in their self-capacity, their resilience in keeping their heritage as they have done for over 600 years? What should be done and to what extent? Who should be responsible for what? These are tricky questions of heritage preservation, far beyond the mere inscription of a site on the famous World Heritage list.

Salt comes from north, gold from south and silver from the land of Whites, but the Word of God, the famous things, histories and fairy tales, we only find them in Timbuktu.

Preserving cultural identity and Korean traditions: The bond of living heritage

It’s the end of November in the countryside near Jeonju, the capital of the North Jeolla Province. The weather is getting chilly and winter is just a couple of weeks away.

It’s time to prepare for the long, icy-cold season. It’s time to make kimchi.

The Republic of Korea’s staple food is a side dish of salted and fermented vegetables that makes its appearance at every meal. It’s not just the country’s emblematic dish: its preparation ( kimjang ) is a community event.

Housewives monitor weather forecasts to determine the most favourable date and temperature for preparing kimchi. Entire families, friends and neighbours gather together to make it. The process is rather laborious and requires many hands to process the large quantities of vegetables required to last throughout the winter months. They all work together, exchange tips and tighten their relationships through kimjang. Families take turns making kimchi to form closer bonds.

Today, the entire village will get together in one of the houses for the occasion. Together, they will wash the napa cabbage that was pickled in salt the night before and mix in the seasonings that will give kimchi its unique sour-and-spicy flavour. The specific methods and ingredients are transmitted from mother to daughter so that kimjang culture is preserved through the generations.

Since 2013, kimjang has been included in UNESCO’s Representative List of the Intangible Cultural Heritage of Humanity as an important part of Korean culture, embodying the country’s cooperative and sharing team spirit. Kimjang is a vital cultural asset of a community and worth preserving and celebrating for the rest of humanity. Even though there may be regional differences in the preparation of kimchi, it transcends class, regional and even national borders.

Cultural practices often precede the instauration of national borders and the start of conflict among its citizens. Shared cultural practices may even be a path to reconciliation. 

Such hopes materialized in 2018, when the Democratic People’s Republic of Korea and the Republic of Korea decided to work together to submit a joint submission for traditional wrestling as an element of UNESCO’s Representative List of the Intangible Cultural Heritage of Humanity.

Ssirum/Ssireum (wrestling) is a physical game and a popular form of entertainment widely enjoyed all across the Korean peninsula. In the North, two opponents try to push each other to the ground using a satpa (a fabric strap connecting the waist and leg), their torso, hands and legs. Ssirum/Ssireum is distinguished by the use of the satpa and the awarding of a bull to the winner. In the South, Ssirum/Ssireum is a type of wrestling in which two players wearing long fabric belts around their waists and one thigh grip their opponents’ belt and deploy various techniques to send them to the ground. The winner of the final game for adults is awarded an ox, symbolizing agricultural abundance, and the title of ‘Jangsa’.

As an approachable sport involving little risk of injury, Ssirum/Ssireum also offers a means to improve mental and physical health. Koreans are widely exposed to Ssirum/Ssireum traditions within their families and local communities: children learn the wrestling skills from family members; local communities hold annual open wrestling tournaments; its instruction is also provided in schools.

Following UNESCO’s mediation, the two States Parties agreed for their respective nomination files to be jointly examined by the Intergovernmental Committee for the Safeguarding of Intangible Cultural Heritage in November 2018. UNESCO welcomed this initiative of regional cooperation and, through a historic decision, inscribed "Traditional Korean wrestling (Ssirum/Ssireum)" on the Representative List of the Intangible Cultural Heritage of Humanity, as a joint inscription from the Democratic People’s Republic of Korea and the Republic of Korea. While the Lists of the Convention include several examples of multinational nominations prepared by several States (from couscous to the art of falconry and the Mediterranean diet), the coming together of the two States Parties for the joint inscription of Korean traditional wrestling by the Committee is unprecedented. It marks a highly symbolic step on the road to inter-Korean reconciliation. It is also a victory for the longstanding and profound ties between both sides of the inter-Korean border, and for the role cultural diplomacy may have in international relations.

It was the time when the women would gather and gossip. There would be matchmaking. There would be some marriages that came about during the time of kimchi making.

Promoting culture in a post-COVID-19 world

The cultural and creative industries are among the fastest growing sectors in the world. With an estimated global worth of US$ 4.3 trillion per year, the culture sector now accounts for 6.1 per cent of the global economy. They generate annual revenues of US$ 2,250 billion and nearly 30 million jobs worldwide, employing more people aged 15 to 29 than any other sector. The cultural and creative industries have become essential for inclusive economic growth, reducing inequalities and achieving the goals set out in the 2030 Sustainable Development Agenda.

The adoption of the 2005 Convention for the Protection and Promotion of the Diversity of Cultural Expressions was a milestone in international cultural policy. Through this historic agreement, the global community formally recognized the dual nature, both cultural and economic, of contemporary cultural expressions produced by artists and cultural professionals. Shaping the design and implementation of policies and measures that support the creation, production, distribution of and access to cultural goods and services, the 2005 Convention is at the heart of the creative economy.

Recognizing the sovereign right of States Parties to maintain, adopt and implement policies to protect and promote the diversity of cultural expression, both nationally and internationally, the 2005 Convention supports governments and civil society in finding policy solutions for emerging challenges.

Based on human rights and fundamental freedoms, the 2005 Convention ultimately provides a new framework for informed, transparent and participatory systems of governance for culture.

A constant rethinking of culture and heritage

The history of UNESCO bears witness to the deep transformation of the concept of culture over the past decades. From global Conventions mostly dealing with building and stones in the 60’s and 70’s, the international cooperation opened new fronts for the protection and promotion of culture, including intangible cultural heritage, cultural diversity and creative economy. The definition of "culture" was spearheaded by the committee led by former UN Secretary-General Javier Pérez de Cuellar and the Mondiacult Conference in 1982. In 2022, the global Mondiacult conference is expected to take stock of progress made in the past 40 years in cultural policies, and re-imagine its future in a post-COVID-19 world.

Have a look at these World Heritage sites

The 30,000-kilometre-long road system was built by the Inca Empire across mountains, valleys, rainforests and deserts to link the Inca capital, Cuzco, with distant areas of the empire, from the Amazon to the Andes. Thanks to its sheer scale, Qhapaq Ñan is a unique achievement of engineering skills, highlighting the Incas' mastery of construction technology.

The granting of World Heritage status in 2019 has made its trail – which every year sees thousands of visitors on their way to the area’s archaeological sites such as Machu Picchu in Peru – eligible for much-needed restoration funds.

Borobudur Temple Compound

Borobudur is the largest Buddhist temple in the world and one of the great archaeological sites of Southeast Asia. This imposing Buddhist temple, dating from the 8th and 9th centuries, is located in central Java. It was built in three tiers: a pyramidal base with five concentric square terraces, the trunk of a cone with three circular platforms and, at the top, a monumental stupa. The walls and balustrades are decorated with fine low reliefs, covering a total surface area of 2,500 m 2 . Around the circular platforms are 72 openwork stupas, each containing a statue of the Buddha. The monument was restored with UNESCO's help in the 1970s.

Bamiyan Valley, Afghanistan

This cultural landscape was simultaneously inscribed on the World Heritage List and the List of World Heritage in Danger in 2003. The property is in a fragile state of conservation, having suffered from abandonment, military action and dynamite explosions. Parts of the site are inaccessible due to the presence of anti-personnel mines.

Related items

• Lists and designations
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• Intangible heritage
• Diversity of Cultural Expressions-2005 Convention
• Intangible Cultural Heritage-2003 Convention
• Underwater Cultural Heritage-2001 Convention
• World Heritage 1972 Convention
• Fight Illicit Trafficking-1970 Convention
• Armed Conflict and Heritage-1954 Convention
• Culture & Sustainable Development
• UNESCO Creative Cities Network

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Food preservation: freezing basics.

Freezing is the easiest, most convenient, and least time-consuming method of preserving foods. Most foods freeze well—with the exception of produce with a high water content, cream-based items, and cooked starchy foods such as cooked noodles and rice. 

All fresh produce contains enzymes, compounds that help the plant ripen and mature. During freezing, enzyme action is slowed but not stopped. If not inactivated, these enzymes can cause color and flavor changes and loss of nutrients during freezer storage. Also, freezing stops, but does not destroy, the microorganisms that cause spoilage or illness.  

Inactivation of Enzymes in Vegetables

Contrary to some publications or folklore, blanching is essential for obtaining top quality frozen vegetables. Blanching vegetables before freezing inactivates the enzymes. During blanching, the vegetable is exposed to boiling water or steam for a brief period. The vegetable is then rapidly cooled in cold water (60 degrees Fahrenheit or below) for the same amount of time to prevent cooking. 

Blanching also helps destroy microorganisms on the surface of the vegetables. When blanched, vegetables such as broccoli and spinach become more compact. Following the recommended times for blanching each vegetable is important. Over-blanching results in a cooked product and loss of flavor, color and nutrients. Under-blanching stimulates enzyme activity and is worse than no blanching at all.

The use of microwave ovens for blanching has become popular. However, microwave blanching is not recommended as it produces uneven results because of varied heat patterns within a microwave oven and from one microwave oven to another. Microwave blanching requires working with only small quantities at a time; there is no time saved when working with large quantities of vegetables.

Prevention of Color Changes in Fruit

Enzymes in fruits can cause browning and loss of Vitamin C. Fruits are not usually blanched. Instead, ascorbic acid (Vitamin C) is used to control enzymes in frozen fruits. Commercial mixtures of ascorbic acid are available for home use. Citric acid or lemon juice also may be used to prevent darkening of fruits, but they are not as effective as ascorbic acid. Packing fruit in sugar or sugar syrup will also control browning, but not as effectively as ascorbic acid.

Prevention of Off Flavors

Another type of change that can occur in frozen products is the development of rancid off flavors. This occurs when fat, such as in meat, is exposed to air over a period of time. It can be controlled by using a storage method that does not allow air to reach the product. Therefore, it is always advisable to remove as much air as possible from the freezer bag or container to reduce the amount of air in contact with the product being frozen.

Freezer Storage

To maintain top quality, store frozen fruits and vegetables at 0 degrees Fahrenheit or lower. The only way to be sure your freezer is at the right temperature is to use a freezer thermometer. Storing frozen foods at temperatures higher than 0 degrees Fahrenheit increases the rate of deterioration and shortens the shelf life of foods. Fluctuating freezer temperatures can cause the ice in the foods to thaw slightly and then refreeze. Every time this happens, the smaller ice crystals form larger ones, further damaging cells and creating a mushier product.

Moisture loss, or ice crystals evaporating from the surface of a product, produces freezer burn—a grainy, brownish spot where the tissues become dry and tough. Freezer-burned food is likely to develop off flavors, but it will not cause illness. Packaging in heavyweight, moisture-resistant materials will prevent freezer burn.

Containers for Freezing

Foods for the freezer should be packed properly to protect their flavor, color, moisture content, and nutritive value. Select packaging materials with these characteristics: 

Suitable packaging materials include rigid plastic containers with straight sides, glass jars made for freezing and canning, heavy-duty aluminum foil, moisture-vapor resistant bags, and freezer paper. Containers intended for short-term storage, such as bread wrap; cottage cheese, milk or ice cream cartons; regular aluminum foil; or waxed paper do not provide effective protection against flavor and moisture loss or freezer burn during long-term storage. Plastic containers designed for long-term freezer storage may or may not be suitable for direct use in a microwave oven.

Packaging Foods

Cool all foods and syrup before packing. Pack foods in quantities that are usable for a single meal.

Pack cold foods tightly into containers. Because most foods expand on freezing, allow ample headspace (space between food and closure). The amount of space needed will vary depending on the food and size of containers. When packing food in bags, press out excess air before sealing. Label and date each package. It is also helpful to list number of servings on the label.

For quick freezing, spread packages among already frozen foods. Leave a small space between packages and add only the amount of unfrozen food to the freezer that will freeze within 24 hours: about 2 to 3 pounds of food to each cubic foot of freezer capacity.

What to Do If Your Freezer Stops

Keep the freezer closed. If it looks like the freezer will be stopped for more than 24 hours, use dry ice (if you can get it) or move the food to another freezer.

CFAES provides research and related educational programs to clientele on a nondiscriminatory basis. For more information, visit cfaesdiversity.osu.edu. For an accessible format of this publication, visit cfaes.osu.edu/accessibility.

Copyright © 2016, The Ohio State University

Water Conservation Essay

500+ words essay on water conservation.

Water makes up 70% of the earth as well as the human body. There are millions of marine species present in today’s world that reside in water. Similarly, humankind also depends on water. All the major industries require water in some form or the other. However, this precious resource is depleting day by day. The majority of the reasons behind it are man-made only. Thus, the need for water conservation is more than ever now. Through this water conservation essay, you will realize how important it is to conserve water and how scarce it has become.

Water Scarcity- A Dangerous Issue

Out of all the water available, only three per cent is freshwater. Therefore, it is essential to use this water wisely and carefully. However, we have been doing the opposite of this till now.

Every day, we keep exploiting water for a variety of purposes. In addition to that, we also keep polluting it day in and day out. The effluents from industries and sewage discharges are dispersed into our water bodies directly.

Moreover, there are little or no facilities left for storing rainwater. Thus, floods have become a common phenomenon. Similarly, there is careless use of fertile soil from riverbeds. It results in flooding as well.

Therefore, you see how humans play a big role in water scarcity. Living in concrete jungles have anyway diminished the green cover. On top of that, we keep on cutting down forests that are a great source of conserving water.

Nowadays, a lot of countries even lack access to clean water. Therefore, water scarcity is a real thing. We must deal with it right away to change the world for our future generations. Water conservation essay will teach you how.

Get the huge list of more than 500 Essay Topics and Ideas

Water Conservation Essay – Conserving Water

Life without water is not possible. We need it for many things including cleaning, cooking, using the washroom, and more. Moreover, we need clean water to lead a healthy life.

We can take many steps to conserve water on a national level as well as an individual level. Firstly, our governments must implement efficient strategies to conserve water. The scientific community must work on advanced agricultural reforms to save water.

Similarly, proper planning of cities and promotion of water conservation through advertisements must be done. On an individual level, we can start by opting for buckets instead of showers or tubs.

Also, we must not use too much electricity. We must start planting more trees and plants. Rainwater harvesting must be made compulsory so we can benefit from the rain as well.

Further, we can also save water by turning off the tap when we brush our teeth or wash our utensils. Use a washing machine when it is fully loaded. Do not waste the water when you wash vegetables or fruit, instead, use it to water plants.

All in all, we must identify water scarcity as a real issue as it is very dangerous. Further, after identifying it, we must make sure to take steps to conserve it. There are many things that we can do on a national level as well as an individual level. So, we must come together now and conserve water.

FAQ of Water Conservation Essay

Question 1: Why has water become scarce?

Answer 1: Water has become scarce due to a lot of reasons most of which are human-made. We exploit water on a daily basis. Industries keep discharging their waste directly into water bodies. Further, sewage keeps polluting the water as well.

Question 2: How can we conserve water?

Answer 2: The government must plan cities properly so our water bodies stay clean. Similarly, water conservation must be promoted through advertisements. On an individual level, we can start by fixing all our leaky taps. Further, we must avoid showers and use buckets instead to save more water.

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Was the Stone Age Actually the Wood Age?

Neanderthals were even better craftsmen than thought, a new analysis of 300,000-year-old wooden tools has revealed.

By Franz Lidz

In 1836, Christian Jürgensen Thomsen, a Danish antiquarian, brought the first semblance of order to prehistory, suggesting that the early hominids of Europe had gone through three stages of technological development that were reflected in the production of tools. The basic chronology — Stone Age to Bronze Age to Iron Age — now underpins the archaeology of most of the Old World (and cartoons like “The Flintstones” and “The Croods”).

Thomsen could well have substituted Wood Age for Stone Age, according to Thomas Terberger, an archaeologist and head of research at the Department of Cultural Heritage of Lower Saxony, in Germany.

“We can probably assume that wooden tools have been around just as long as stone ones, that is, two and a half or three million years,“ he said. “But since wood deteriorates and rarely survives, preservation bias distorts our view of antiquity.” Primitive stone implements have traditionally characterized the Lower Paleolithic period, which lasted from about 2.7 million years ago to 200,000 years ago. Of the thousands of archaeological sites that can be traced to the era, wood has been recovered from fewer than 10.

Dr. Terberger was team leader of a study published last month in the Proceedings of the National Academy of Sciences that provided the first comprehensive report on the wooden objects excavated from 1994 to 2008 in the peat of an open-pit coal mine near Schöningen, in northern Germany. The rich haul included two dozen complete or fragmented spears (each about as tall as an N.B.A. center) and double-pointed throwing sticks (half the length of a pool cue) but no hominid bones. The objects date from the end of a warm interglacial period 300,000 years ago, about when early Neanderthals were supplanting Homo heidelbergensis, their immediate predecessors in Europe. The projectiles unearthed at the Schöningen site, known as Spear Horizon, are considered the oldest preserved hunting weapons.

In the mid-1990s, the discovery of three of the spears — along with stone tools and the butchered remains of 10 wild horses — upended prevailing ideas about the intelligence, social interaction and toolmaking skills of our extinct human ancestors. At the time, the scientific consensus was that humans were simple scavengers who lived hand-to-mouth until about 40,000 years ago.

“It turned out that these pre-Homo sapiens had fashioned tools and weapons to hunt big game,” Dr. Terberger said. “Not only did they communicate together to topple prey, but they were sophisticated enough to organize the butchering and roasting.”

The new study, which began in 2021, examined more than 700 pieces of wood from the Spear Horizon, many of which had spent the previous two decades stored in chilled tubs of distilled water to simulate the waterlogged sediment that had protected them from decay. With the aid of 3-D microscopy and micro-CT scanners that highlighted signs of wear or cut marks, researchers identified 187 pieces of wood that showed evidence of splitting, scraping or abrasion.

“Until now, splitting wood was thought to have been only practiced by modern humans,” said Dirk Leder, an archaeologist also at Lower Saxony and lead author of the paper.

Besides weapons, the assemblage included 35 pointed and rounded artifacts that were most likely used in domestic activities such as punching holes and smoothing hides. All were carved from spruce, pine or larch — “woods that are both hard and flexible,” said Annemieke Milks, an anthropologist from the University of Reading who collaborated on the project.

Since neither spruce nor pine would have been available at the lakeshore, where the site was located, the research team deduced that the trees had been felled on a mountain two or three miles away or perhaps even farther. Close inspection of the spears indicated that the Stone Agers planned their woodworking projects carefully, following a set order: strip the bark, remove the branches, sharpen the spear head, harden the wood in fire. “The wooden tools had a higher level of technological complexity than we usually see in stone tools from that age,” Dr. Leder said.

Francesco d’Errico, an archaeologist at University of Bordeaux who was not involved in the study, praised its insights into the methods and materials that Stone Age people used to solve practical Stone Age problems. “The paper opens a window into the almost unknown world of the Lower Paleolithic,” he said. “In spite of the paucity of data, the authors make a courageous attempt to propose a scenario for the evolution of such technology that needs to be tested in the future against new discoveries.”

Perhaps the most surprising revelation is that some of the spear points were resharpened after earlier breakage or dulling, and that some of the broken weapons had been whittled down, polished and repurposed. “The wood that we identified as working debris suggested that tools were repaired and recycled into new tools for other tasks,” Dr. Milks said.

All but one of the spears were hewed from the trunks of slow-growing spruce trees and shaped and balanced like modern javelins, with the center of gravity in the middle of the shaft. But were they meant for throwing, or for thrusting? “The spears were made from dense wood and with thick diameters,” Dr. Milks said. “To me, that suggests the hominids manufacturing them may have intentionally designed at least some as flight weapons for hunting.”

She tested the spears’ external ballistics by enlisting six trained male javelin throwers, aged 18 to 34, to heave replicas at hay bales from various distances. “My point was to ask people who were a little bit better at doing this than archaeologists, because up until that point, we’d had experiments with lots of people who were … archaeologists,” Dr. Milks said, adding: “Anthropologists are not very good at that kind of thing, either.”

From 33 feet away, Team Neanderthals hit the target 25 percent of the time. The athletes were equally accurate at 50 feet, and only slightly less (17 percent) at 65 feet. “Still, that was double the range at which scientists had estimated a hand-thrown spear could be useful for hunting,” Dr. Milks said.

For her, the notion that our Stone Age forebears were artisans serves to humanize them. “Working wood is slow, even if you’re good at it,” she said. “There are lots of different steps in the process.” She imagines a bunch of Neanderthals clustered around an evening campfire, assembling and sanding and mending their wooden handicrafts. “It all seems very, very close, in a way,” she said, wistfully, “even though it was such a long, long time ago.”