Preservation Of Food

Preservation Of Food
Food spoilage is brought about by the action of enzymes present in foods due to the act of microorganisms such as mold, yeast, and bacteria or due to infestation with insects and worms. The environment unfavorable to the activity of enzymes or the growth of microorganisms is the main objective of food preservation.

Natural and artificial methods are adopted for this purpose. Preservatives are also added to foods to preserve them. Various agents are used to bring either physical or chemical changes in food materials to be held.

As the principal spoilage agents usually are present in foods, destroying them or preventing their development becomes the chief problem of food preservation. Any condition opposed to the development of these organisms, whether by retarding their growth or by destroying them, aids in the protection of food.

Methods commonly used include shared or cellar storage, refrigeration, canning, freezing, preservatives, drying, and excluding air. However, not a widely used way at present, “cold sterilization” or irradiation by beta and gamma rays to prolong the keeping quality of foods, is being widely studied experimentally. The possibilities of this method of food preservation are great. When some of the major problems now limiting its use are solved, radical changes will probably be in the presently accepted food handling methods.

Refrigeration: Microorganisms, although not readily destroyed by severe cold, are much less active at low temperatures. Refrigeration is widely used in homes and commercial plants to maintain the low temperature found satisfactory in the storage of perishable foods. Fresh milk, meat, and similar foods are kept just above freezing.

Certain fruits and vegetables also keep better when cold, although, as a rule, they do not require low temperatures for the limited time they are stored in the home, as do the protein foods cited. Under-ripe fruits usually ripen rapidly at room temperature. The keeping of cooked foods and leftovers is greatly facilitated by refrigeration, which is a more expensive but more efficient preservation method than standard storage.

Wrapping certain fruits and vegetables in paper or cellophane, or coating them with wax, improves the keeping quality. Pears and apples of high quality are to be kept for winter use, and oranges, lemons, and grapefruit are often wrapped. The fruit or the paper in which it is wrapped may be treated to retard mold formation. Green peppers, tomatoes, oranges and other citrus fruits, cucumbers, and cantaloupes are among the foods whose keeping quality is improved when coated with wax.

Heating: Food is commonly preserved through the application of high temperatures. A temperature considerably above that of the body may result in either a pasteurized or a sterilized product. Foods are commonly pasteurized by being held at a temperature of 60o to 66o C for thirty to forty minutes, during which most of the organisms, although not all, are killed. Spores and some vegetative forms of bacteria remain, but as a rule, those causing diseases are destroyed. This method is used for the temporary preservation of milk and fruit juices, and other fruit products of delicate flavor. Acid foods are rendered sterile by boiling for a comparatively short time.

Canning: If the effectiveness of pasteurization and sterilization is to extend over some time of practical significance, the material thus treated must be protected from fresh contamination by microorganisms. In canning, sterilized or pasteurized food is afforded such. Protection accounts, at least in part, for the rapid growth in popularity of the process for food preservation. The first foods preserved % in nine canning were sealed in glass.

All prejudice that once existed against canned foods has been removed. Experiments have shown canned foods to be as wholesome as any preserved food. Often canned food is superior in food value to freshly cooked. Canned foods are ready to use at a moment’s notice. When food is to be kept over a long period, canned products are also most satisfactory, and they do not require exceptional temperatures or equipment for storage.

Freezing: Freezing, like cold storage, does not destroy the microorganisms enzymes in the foods. However, it does render them more or less inactive so that frozen foods, when held at the proper temperature, change slowly. This applies to the nutritional value and other chemical and physical characteristics.

Practically all common fruits are now preserved by freezing. However, the success with which the different fruits can be frozen varies. Most of the vegetables that are served cooked may be held by freezing. Scalding to destroy the enzymes is essential for successfully preserving almost all vegetables by this method.

Hence, fresh and crisp vegetables in salads cannot be preserved by freezing. Fish, poultry, and game, as well as beef, veal, pork, and lamb, will be held by freezing. Frozen foods have little or no waste when used, and little time is required for preparation. However, time must allow for the thawing of fruits to be served raw, and the cooking period of frozen meats and vegetables not already defrosted must be sufficient for both thawing and cooking.

Using Chemical Preservatives: Certain chemicals help preserve foods, either by retarding or preventing the growth of microorganisms. These may be added to the product or produced in it by fermentation. Sugar, a common preservative, is often used in such quantities as to increase the concentration of the food and make it an unfavorable medium for organisms. Salt and acid, in the form of vinegar or lemon juice, are substances added for their preservative action. Frequently, the fermentation process is used to produce acetic lactic within the food itself that exerts the same preservative action as is obtained by adding vinegar.

Salt is used as an aid in the preservation of vegetables by fermentation. It aids both in drawing out the juices that are delaying the action of specific spoilage agents. Formerly, spices were often used in such quantities as to have a definite preservative effect. Today the concentration in which they are used is usually less than employed earlier, and it is believed that only a few of them are of value as preservatives.

Certain preservatives such as borax, boric acid, sulfites, and formaldehyde, once sold as canning powders, are now considered harmful to human beings, and their use is usually prohibited.

Preserving and Pickling: Preserving and pickling are methods of preservation frequently employed. Long before canning was known as a means of preserving foods, preservatives were practiced. The salting of foods was an early method of conservation. Salt is a valuable preservative as an antiseptic and an agent for removing water. Placing foods in a brine of a specific concentration promotes fermentation, and the foods develop a mellow flavor. Sugar in large amounts is likewise a favorite preservative. Today, although practically every known variety of preserves and pickles are found in the market, the distinctive flavor of the homemade product is often preserved.

Drying: Removal of moisture is of benefit in preserving food. Although it is challenging to dry foods to the point of destroying microorganisms, it is comparatively easy to dry foods so that no spoilage takes place. All organisms must have food to develop and grow; before the food is available to them, it must be in a relatively dilute solution.

These microorganisms obtain food by osmotic action. Drying foods to prevent spoilage does not necessarily mean complete removal of the water, but it does mean concentration to such a point that the liquid is denser than the body fluid of the organisms. When the liquid outside the cell wall is thick than that inside, the liquid within tends to be removed from the cell, and the body processes are delayed or prevented.

Hence, although the food is present, it may not be available to the organism, which might cause spoilage. Drying may retard enzyme action also, but in vegetables especially, the effect of enzymes is sufficient to cause comparatively rapid deterioration. Scalding to destroy enzymes is highly beneficial in prolonging the storage life of dehydrated vegetables. Drying dramatically alters the character of the food and requires some time for preparation both before and after the process.

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