Food Preservation
The process of treating and handling food in a way to stop or cut down spoilage to prevent the foodborne illness without hampering the texture, nutritional value and flavour is called as food preservation. In oher words food preservation is method of preparing food to be dtored for future use. Food preservation is practiced from tha early ages to make food edible for a long time. The food preserved in early times were cheese, butter, raisins, pemmican, sausage, bacon and grains.Food preservation involves preventing the growth of bacteria, fungi and other micro-organisms and retarding the oxidation of fats causing rancidity. Food preservation to a great extent means preventing the contamination of food substances.

Preservation processes include:

  • Heating to kill or denature organisms (e.g. boiling)
  • Oxidation (e.g use of sulphur dioxide)
  • Toxic inhibition (e.g. smoking, use of carbon dioxide, vinegar, alcohol etc)
  • Dehydration (drying)
  • Osmotic inhibition ( e.g use of syrups)
  • Low temperature inactivation (e.g. freezing)
  • Ultra high water pressure (e.g. fresherized, a kind of “cold” pasteurization, the pressure kills naturally occurring pathogens, which cause food deterioration and affect food safety.)
  • Many combinations of these methods
  • Chelation

Preserved food

Food Preservation Methods

Drying
One of the oldest methods of food preservation is by drying, which reduces water activity sufficiently to delay or prevent bacterial growth. Most types of meat can be dried. This is especially valuable in the case of pig meat, since it is difficult to keep without preservation. Many fruits can also be dried; for example, the process is often applied to apples, pears, bananas, mangos, papaya, and coconut. Zante currants, sultanas and raisins are all forms of dried grapes. Drying is also the normal means of preservation for cereal grains such as wheat, maize, oats, barley, rice, millet and rye.

Smoking
Meat, fish and some other foods may be both preserved and flavoured through the use of smoke, typically in a smoke-house. The combination of heat to dry the food without cooking it, and the addition of the aromatic hydrocarbons from the smoke preserves the food.

Freezing
Freezing is also one of the most commonly used processes commercially and domestically for preserving a very wide range of food stuffs including prepared food stuffs which would not have required freezing in their unprepared state. For example, potato waffles are stored in the freezer, but potatoes themselves require only a cool dark place to ensure many months' storage. Cold stores provide large volume, long-term storage for strategic food stocks held in case of national emergency in many countries.

Vacuum Packing

Vacuum-packing stores food in a vacuum environment, usually in an air-tight bag or bottle. The vacuum environment strips bacteria of oxygen needed for survival, hence preventing the food from spoiling. Vacuum-packing is commonly used for storing nuts.

Salt
Salting or curing draws moisture from the meat through a process of osmosis. Meat is cured with salt or sugar, or a combination of the two. Nitrates and nitrites are also often used to cure meat.

Sugar
Sugar is used to preserve fruits, either in syrup with fruit such as apples, pears, peaches, apricots, plums or in crystallised form where the preserved material is cooked in sugar to the point of crystralisation and the resultant product is then stored dry. This method is used for the skins of citrus fruit (candied peel), angelica and ginger. A modification of this process produces glacé fruit such as glacé cherries where the fruit is preserved in sugar but is then extracted from the syrup and sold, the preservation being maintained by the sugar content of the fruit and the superficial coating of syrup. The use of sugar is often combined with alcohol for preservation of luxury products such as fruit in brandy or other spirits. These should not be confused with fruit flavoured spirits such as Cherry Brandy or Sloe gin

Pickling
Pickling is a method of preserving food by placing it or cooking it in a substance that inhibits or kills bacteria and other micro-organisms. This material must also be fit for human consumption. Typical pickling agents include brine (high in salt), vinegar, ethanol, and vegetable oil, especially olive oil but also many other oils. Most pickling processes also involve heating or boiling so that the food being preserved becomes saturated with the pickling agent. Frequently pickled items include vegetables such as cabbage (to make sauerkraut and curtido), peppers, and some animal products such as corned beef and eggs. EDTA may also be added to chelate calcium. Calcium is essential for bacterial growth.

Lye
Sodium hydroxide (lye)makes food too alkaline for bacterial growth. Lye will saponify fats in the food, which will change its flavor and texture. Lutefisk and hominy use lye in their preparation, as do some olive recipes.

Canning and Bottling
Canning involves cooking fruits or vegetables, sealing them in sterile cans or jars, and boiling the containers to kill or weaken any remaining bacteria as a form of pasteurization. Various foods have varying degrees of natural protection against spoilage and may require that the final step occur in a pressure cooker. High-acid fruits like strawberries require no preservatives to can and only a short boiling cycle, whereas marginal fruits such as tomatoes require longer boiling and addition of other acidic elements. Many vegetables 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 causes gas production and the can will swell or burst. However, there have been examples of poor manufacture and poor hygiene allowing contamination of canned food by the obligate , 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. Food contaminated in this way has included Corned beef and Tuna.


Various preserved foods


                                                                                                                       

Jellying

Food may be preserved by cooking in a material that solidifies to form a gel. Such materials include gelatine, agar, maize flour and arrowroot flour. Some foods naturally form a protein gel when cooked such as eels and elvers, and sipunculid worms which are a delicacy in the town of Xiamen in Fujian province of the People's Republic of China. Jellied eels are a delicacy in the East End of London where they are eaten with mashed potatoes. Potted meats in aspic, (a gel made from gelatine and clarified meat broth) were a common way of serving meat off-cuts in the UK until the 1950s

Meat can be preserved by jugging, the process of stewing the meat (commonly game or fish) in a covered earthenware jug or casserole. The animal to be jugged is usually cut into pieces, placed into a tightly-sealed jug with brine or gravy, and stewed. Red wine and/or the animal's own blood is sometimes added to the cooking liquid. Jugging was a popular method of preserving meat up until the middle of the 20th century.

Irradiation
Irradiation of food is the processing of food with ionizing radiation; either high-energy electrons or X-rays from accelerators, or by gamma rays (emitted from radioactive sources as Cobalt-60 or Caesium-137). The treatment has a range of effects, including killing bacteria, molds and insect pests, reducing the ripening and spoiling of fruits, and at higher doses inducing sterility. The technology may be compared to pasteurization; it is sometimes called 'cold pasteurization', as the product is not heated. Irradiation is not effective against viruses or prions, and is only useful for food of high initial quality.

As any other technology it is not a panacea and cannot resolve food problems in general. Only food of high initial quality is suitable for radiation processing; a spoiled food cannot be reverted to un-spoiled. Irradiation is not effective against viruses and prions; it cannot eliminate toxins already formed by microorganisms.

The radiation process is unrelated to nuclear energy, but it may use the radiation emitted from radioactive nuclides produced in nuclear reactors. Ionizing radiation is hazardous to life; for this reason irradiation facilities have a heavily shielded irradiation room where the process takes place. Radiation safety procedures ensure that neither the workers in such facility nor the environment receive any radiation dose from the facility. Irradiated food does not become radioactive, and national and international expert bodies have declared food irradiation as wholesome. However, the wholesomeness of consuming such food is disputed by opponents and consumer organizations. [1] National and international expert bodies have declared food irradiation as 'wholesome'; UN-organizations as WHO and FAO are endorsing to utilize food irradadiation. International legislature on whether food may be irradiated or not varies worldwide from no regulation to full banning.[2]

It is estimated that about 500,000 tons of food items are irradiated per year world-wide in over 40 countries. These are mainly spices and condiments with an increasing segment of fresh fruit irradiated for fruit fly quarantine[3][4].

Modified atmosphere

Modified atmosphere is a way to preserve food operating on the atmosphere around it. Salad crops which are notoriously difficult to preserve are now being packaged in sealed bags with an atmosphere modified to reduce the oxygen (O2) concentration and increase the carbon dioxide (CO2) concentration. There is concern that although salad vegetables retain their appearance and texture in such conditions, this method of preservation may not retain nutrients, especially vitamins.

Grains may be preserved using carbon dioxide. A block of dry ice is placed in the bottom and the can is filled with grain. The can is then "burped" of excess gas. The carbon dioxide from the sublimation of the dry ice prevents insects, mold, and oxidation from damaging the grain. Grain stored in this way can remain edible for five years.

Nitrogen gas (N2) at concentrations of 98% or higher is also used effectively to kill insects in grain through hypoxia. However, carbon dioxide has an advantage in this respect as it kills organisms through both hypoxia and hypercarbia, requiring concentrations of only 80%, or so. This makes carbon dioxide preferable for fumigation in situations where an hermetic seal cannot be maintained.

Clamps
Many root vegetables are very resistant to spoilage and require no other preservation other than storage in cool dark conditions, usually in field clamps.

Biological processes
Some foods, such as many traditional cheeses, will keep for a long time without use of any special procedures. The preservation occurs because of the presence in very high numbers of beneficial bacteria or fungi which use their own biological defences to prevent other organisms gaining a foot-hold.

Fresherized process

An ultra-high pressure food preservation technique using water pressure of approximately 50-100,000 pounds per square inch, equivalent to 3-6 times the pressure found at the bottom of the ocean. A kind of “cold” pasteurization, the pressure kills naturally occurring pathogens, which cause food deterioration and affect food safety.

Fresherized food is different than other methods of food preservation which use heat pasteurization and chemical additives. The taste, texture and naturally occurring vitamins are equal to “freshly made” food. In addition, the amount of energy used for fresherized foods is relatively low, compared to food preservation methods that require heat.

Advantages and disadvantages of Food Preservation Methods
Drying
Advantages :

  • Produces concentrated form of food.
  • Inhibits microbial growth & autolytic enzymes.
  • Retains most nutrients.

Disadvantages:

  • Can cause loss of some nutrients, particularly thiamin & vitamin C.
  • Sulphur dioxide is sometimes added to dried fruits to retain vitamin C, but some individuals are sensitive to this substance.

Smoking
Advantages :

  • Preserve partly by drying, partly by incorporation of substances from smoke.

Disadvantages:

  • Eating a lot of smoked foods has been linked with some cancers in some parts of the world.

Refrigeration
Advantages

  • Slows microbial multiplication.
  • Slows autolysis by enzymes.

Disadvantages:

  • Slow loss of some nutrients with time

Freezing    
Advantages

  • Prevents microbial growth by low temperature & unavailability of water.
  • Generally good retention of nutrients.

Disadvantages:

  • Blanching of vegetables prior to freezing causes loss of some B-Group vitamins and vitamin C.
  • Unintended thawing can reduce product quality.

Adding Salt or Sugar
Advantages

  • Makes water unavailable for microbial growth.
  • Process does not destroy nutrients.

Disadvantages:

  • Increases salt and sugar content of food.
  • High heat processing (e.g. pasteurisation)

Advantages

  • Inactivates autolytic enzymes
  • Destroys microorganisms.

Disadvantages:

  • Loss of heat-sensitive nutrients.

Canning (involves high heat processing)
Advantages

  • Destroys microorganisms & autolytic enzymes.

Disadvantages:

  • Water-soluble nutrients can be lost into liquid in can.

Chemical Preservatives
Advantages

  • Prevent microbial growth
  • No loss of nutrient.

Disadvantages:

  • Some people are sensitive to some chemical preservatives.

Ionizing Radiation
Advantages

  • Sterilizes foods (such as spices) whose flavour would change with heating.
  • Inhibits sprouting potatoes
  • Extends shelf life of strawberries and mushrooms

Disadvantages:

  • Longer shelf life of fresh foods can lead to greater nutrient losses than if eaten sooner after harvesting.
Various Preserved Foods