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Food preservation includes processes that make food more resistant to microorganism growth and slow the redox of . This slows down the decomposition and rancidification process. Food preservation may also include processes that inhibit visual deterioration, such as the enzymatic browning reaction in apples after they are cut during food preparation. By preserving food, food waste can be reduced, which is an important way to decrease production costs and increase the efficiency of , improve food security and nutrition and contribute towards environmental sustainability. For instance, it can reduce the environmental impact of food production.
Many processes designed to preserve food involve more than one food preservation method. Preserving fruit by turning it into jam, for example, involves boiling (to reduce the fruit's moisture content and to kill bacteria, etc.), sugaring (to prevent their re-growth) and sealing within an airtight jar (to prevent recontamination).
Different food preservation methods have different impacts on the quality of the food and food systems. Some traditional methods of preserving food have been shown to have a lower Waste hierarchy and carbon footprint compared to modern methods. Some methods of food preservation are also known to create .
Many root vegetables are very resistant to spoilage and require no other preservation than storage in cool dark conditions, for example by burial in the ground, such as in a storage clamp (not to be confused with a root cellar). Cabbage was traditionally buried during autumn in northern US farms for preservation. Some methods keep it crispy while other methods produce sauerkraut. A similar process is used in the traditional production of kimchi.
Sometimes meat is buried under conditions that cause preservation. If buried on hot coals or ashes, the heat can kill pathogens, the dry ash can desiccate, and the earth can block oxygen and further contamination. If buried where the earth is very cold, the earth acts like a refrigerator, or, in areas of permafrost, a freezer.
In Odisha, India, it is practical to store rice by burying it underground. This method helps to store for three to six months during the dry season.
Butter and similar substances have been preserved as bog butter in Irish peat bogs for centuries. are traditionally created by placing eggs in alkaline mud (or other alkaline substance), resulting in their "inorganic" fermentation through raised pH instead of spoiling. The fermentation preserves them and breaks down some of the complex, less flavorful proteins and fats into simpler, more flavorful ones.
Foods have varying degrees of natural protection against spoilage and may require that the final step occurs in a pressure cooker. High-acid fruits like Strawberry require no preservatives to can and only a short boiling cycle, whereas marginal vegetables such as require longer boiling and the addition of other acidic elements. Low-acid foods, such as vegetables and meats, require pressure canning. Food preserved by canning or bottling is at immediate risk of spoilage once the can or bottle has been opened.
Lack of quality control in the canning process may allow ingress of water or micro-organisms. Most such failures are rapidly detected as decomposition within the can cause gas production and the can will swell or burst. However, there have been examples of poor manufacture (underprocessing) and poor hygiene allowing contamination of canned food by the obligate anaerobe Clostridium botulinum, which produces an acute toxin within the food, leading to severe illness or death. This organism produces no gas or obvious taste and remains undetected by taste or smell. Its toxin is denatured by cooking, however. Cooked , when handled poorly and then canned, can support the growth of Staphylococcus aureus, which produces a toxin that is not destroyed by canning or subsequent reheating.
Before the era of mechanical refrigeration, cooling for food storage occurred in the forms of and . Rural people often did their own ice cutting, whereas town and city dwellers often relied on the ice trade. Today, root cellaring remains popular among people who value various goals, including local food, heirloom plant, traditional home cooking techniques, , frugality, self-sufficiency, organic farming, and others.
In 2015, the International Agency for Research on Cancer of the World Health Organization classified processed meat—i.e., meat that has undergone salting, curing, and smoking—as "carcinogenic to humans".
Methods of fermentation include, but are not limited to, starter microorganisms, salt, hops, controlled (usually cool) temperatures and controlled (usually low) levels of oxygen. These methods are used to create the specific controlled conditions that will support the desirable organisms that produce food fit for human consumption. Fermentation is the microbial conversion of starch and sugars into alcohol. Not only can fermentation produce alcohol, but it can also be a valuable preservation technique. Fermentation can also make foods more nutritious and palatable.
Water was also turned into alcoholic beverages through fermentation. When water is used to make beer, the boiling during the brewing process may kill bacteria that could make people sick. The barley and other ingredients also infuse the drink with nutrients, and the microorganisms can also produce vitamins as they ferment. However, the common belief that premodern people avoided drinking ordinary water is a myth. While people avoided drinking dirty or polluted water, they also avoided using it for the production of beer and wine. Water was visually inspected, smelled, tasted, filtered, and boiled if necessary. It was used for drinking as well as for diluting wine, cooking, and many other processes.
Some animal flesh forms a protein gel when cooked. Eel, and Sipuncula worms, are a delicacy in Xiamen, China, as are in the East End of London, where they are eaten with mashed potatoes. British cuisine has a rich tradition of . Meat off-cuts were, until the 1950s, preserved in aspic, a gel made from gelatin and clarified meat broth. Another form of preservation is setting the cooked food in a container and covering it with a layer of fat. Potted chicken liver can be prepared in this way, and so can potted shrimps, to be served on toast. Calf's foot jelly used to be prepared for invalids.
Jellying is one of the steps in producing traditional pâtés. Many jugging (see below) are also jellied.
Another type of jellying is fruit preserves, which are preparations of cooked fruits, vegetables and sugar, often stored in glass jam jars and . Many varieties of fruit preserves are made globally, including sweet fruit preserves, such as those made from strawberry or apricot, and savory preserves, such as those made from tomatoes or squash. The ingredients used and how they are prepared determine the type of preserves; , jellies, and are all examples of different styles of fruit preserves that vary based upon the fruit used. In English, the word preserves, in plural form, is used to describe all types of jams and jellies.
In chemical pickling, the food is placed in an edible liquid that inhibits or kills bacteria and other microorganisms. Typical pickling agents include brine (high in salt), vinegar, ethanol, and vegetable oil. Many chemical pickling processes also involve heating or boiling so that the food being preserved becomes saturated with the pickling agent. Common chemically pickled foods include Pickled cucumber, capsicum, corned beef, herring, and Pickled egg, as well as mixed vegetables such as piccalilli.
In fermentation pickling, bacteria in the liquid produce as preservation agents, typically by a process that produces lactic acid through the presence of lactobacillales. Fermented pickles include sauerkraut, nukazuke, kimchi, and surströmming.
In northern climates without sufficient sun to dry foods, preserves are made by heating the fruit with sugar. Sugar is used to preserve fruits, either in an antimicrobial syrup with fruit such as apples, pears, peaches, apricots, and plums, or in crystallized form where the preserved material is cooked in sugar to the point of crystallization and the resultant product is then stored dry. The latter method is used for the skins of citrus fruit (candied peel), angelica, and ginger.
Besides UHT, aseptic processing may be used in conjunction with any of the microbe-reduction technologies listed below. With pasteurization and "high pressure pasteurization", the food may not be completely sterilized (instead achieving a specified log reduction), but the use of sterile packaging and environments is retained.
There is also another approach of impregnating packaging materials (plastic films or other) with antioxidants and antimicrobials. (2026). 9780367397289, CRC Press. ISBN 9780367397289
National and international expert bodies have declared food irradiation as "wholesome"; organizations of the United Nations, such as the World Health Organization and Food and Agriculture Organization, endorse food irradiation.World Health Organization. Wholesomeness of irradiated food. Geneva, Technical Report Series No. 659, 1981World Health Organization. High-Dose Irradiation: Wholesomeness of Food Irradiated With Doses Above 10 kGy. Report of a Joint FAO/IAEA/WHO Study Group. Geneva, Switzerland: World Health Organization; 1999. WHO Technical Report Series No. 890 Consumers may have a negative view of irradiated food based on the misconception that such food is radioactive;Conley, S.T., What do consumers think about irradiated foods, FSIS Food Safety Review (Fall 1992), 11–15 in fact, irradiated food does not and cannot become radioactive. Activists have also opposed food irradiation for other reasons, for example, arguing that irradiation can be used to sterilize contaminated food without resolving the underlying cause of the contamination.Hauter, W. & Worth, M., Zapped! Irradiation and the Death of Food, Food & Water Watch Press, Washington, DC, 2008 International legislation on whether food may be irradiated or not varies worldwide from no regulation to a full ban. NUCLEUS – Food Irradiation Clearances
Approximately 500,000 tons of food items are irradiated per year worldwide in over 40 countries. These are mainly and , with an increasing segment of fresh fruit irradiated for fruit fly quarantine. Food irradiation – Position of ADA J Am Diet Assoc. 2000;100:246-253 C.M. Deeley, M. Gao, R. Hunter, D.A.E. Ehlermann, The development of food irradiation in the Asia Pacific, the Americas and Europe; tutorial presented to the International Meeting on Radiation Processing, Kuala Lumpur, 2006.
Lactic acid bacteria (LAB) have antagonistic properties that make them particularly useful as biopreservatives. When LABs compete for nutrients, their often include active antimicrobials such as lactic acid, acetic acid, hydrogen peroxide, and peptide . Some LABs produce the antimicrobial nisin, which is a particularly effective preservative.FAO: Preservation techniques Fisheries and aquaculture department, Rome. Updated 27 May 2005. Retrieved 14 March 2011.Alzamora SM, Tapia MS and López-Malo A (2000) Minimally processed fruits and vegetables: fundamental aspects and applications Springer, p. 266. .
LAB bacteriocins are used in the present day as an integral part of hurdle technology. Using them in combination with other preservative techniques can effectively control spoilage bacteria and other pathogens, and can inhibit the activities of a wide spectrum of organisms, including inherently resistant Gram-negative bacteria.
Hurdle technology has been defined by Leistner (2000) as an intelligent combination of hurdles that secures the microbial safety and stability as well as the organoleptic and nutritional quality and the economic viability of .Leistner I (2000) "Basic aspects of food preservation by hurdle technology" International Journal of Food Microbiology, 55:181–186. The organoleptic quality of the food refers to its sensory properties, that is its look, taste, smell, and texture.
Examples of hurdles in a food system are high temperature during processing, low temperature during storage, increasing the acidity, lowering the water activity or redox potential, and the presence of or . According to the type of pathogens and how risky they are, the intensity of the hurdles can be adjusted individually to meet consumer preferences in an economical way, without sacrificing the safety of the product.Alasalvar C (2010) Seafood Quality, Safety and Health Applications John Wiley and Sons, Page 203. .
| + Principal hurdles used for food preservation (after Leistner, 1995)Leistner L (1995) "Principles and applications of hurdle technology" In Gould GW (Ed.) New Methods of Food Preservation, Springer, pp. 1–21. .Lee S (2004) "Microbial Safety of Pickled Fruits and Vegetables and Hurdle Technology" Internet Journal of Food Safety, 4: 21–32. | ||
| High temperature | F | Heating |
| Low temperature | T | Refrigeration, Frozen food |
| Reduced water activity | a | Drying, curing, conserving |
| Increased acidity | pH | Acid addition or formation |
| Reduced redox potential | E | Removal of oxygen or addition of ascorbate |
| Competitive flora such as microbial fermentation | ||
| Other | , , |
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