Foods, Preserved

food products of plant or animal origin that are specially treated to survive prolonged periods of storage.

Preserved foods are packed and hermetically sealed in metal (tin, aluminum), glass, or polymer containers and treated thermally to destroy or suppress the vital activities of microorganisms that could cause spoilage. The process preserves the nutritional value of the products, the caloric content, and the mineral content. The vitamin content is decreased only insignificantly. Moreover, the process of preparation and preserving increases the quality of many products by removing inedible parts and adding fats (for example, in sautèing fish or vegetables) or sugar (in making preserves and jams). The basic components of the foods are altered only insignificantly during prolonged storage. The loss of the most unstable compounds, the vitamins, is even lower for preserved foods than is that incurred while cooking ordinary dishes from the same raw ingredients. The principal indexes of the nutritive value of some preserved foods are shown in Table 1.

More than 800 types of preserved foods are produced in the USSR. These include meat, dairy, fish, vegetable, and fruit items. Meats are preserved in a number of forms: plain meats (stewed beef, pork, and mutton; roasted chicken, duck, and goose in their own gravy); special ready-made meat and poultry dishes (chicken ragout en gelée; chakhokhbili [a Georgian chicken dish], chicken in white sauce); pâtés (meat, pork, liver); goulash and beef Stroganoff; sausages, kolbasy [a kind of sausage], and kolbasy stuffings (tongue, ham, sausage); and organ meats (kidneys, brains, chitterlings). Preserved combination meat-vegetable products include meat with peas, beans, lentils, groats, and macaroni products. Preserved meat and meat-vegetable products are usually packed in small containers (0.3-0.5 liters [l]; never larger than 3l), since to be effective, their sterilization must be prolonged and at high temperatures.

Preserved dairy items include condensed products with sugar (milk, cream, skim milk) and sterilized condensed milk without sugar. The items in the first group need not be sterilized, since the high sugar concentration keeps them from spoiling. For this reason they are packaged not only in small tin containers but also in large metal and wooden containers (jars, barrels) for largescale consumers and for further industrial processing (in the bread, confectionery, and ice cream industries).

Fish may be preserved in a number of forms: plain fish (salmon, sturgeon, crab, shrimp, trepang, squid, and mussel in its own juice); fish dishes cooked in tomato sauce or oil; and smoked fish. All of these items are sterilized. In addition, there are unsterilized fish products, including sprats, sardines, and herring in a variety of spicy salt and other pungent marinades. All of these items must be refrigerated (at no greater than 5°C) and last no longer than six months.

Vegetables too are preserved in a variety of ways: plain vegetables (carrots, beets, cauliflower, asparagus, green peas, whole tomatoes, cucumbers, sweet corn, beans, sorrel); juices (tomato, carrot, beet); concentrated tomato products (paste, purée, sauces); appetizers, such as eggplant, pumpkin, carrot, and onion cooked in vegetable oil; stuffed vegetables, stuffed cabbage, sliced vegetables, and vegetable pastes, ready-made first- and second-course dishes (borscht, shchi [cabbage soup], solianka [stewed cabbage with fish], vegetable ragout); pasteurized or sterilized pickled and marinated vegetables; baby foods, mainly pureed or finely strained (homogenized); and dietetic vegetables, prepared according to special recipes for people suffering from certain ailments. The preserved vegetable products also include sauces, seasonings, and products made from mushrooms.

Preserved fruit products include plain canned fruits, compotes made of fresh fruits and berries with sugar, and sterilized purees, juices (clear, clarified, or with pulp or tiny pieces of fruit), pre-serves, jams, jellies, and syrups. Fruits, berries, and vegetables are also frozen.

The operative standard in the USSR provides for a single system of labeling the various containers (mainly the tins). This takes the form of a letter and number code, in effect an identity card for the container. Each plant is assigned a certain number that, in combination with the letter index (M for meat and dairy plants, R for fish, and K for fruit and vegetable enterprises), makes it possible to determine the origin of each container of preserved food. Each is also marked with a batch number and with the date and shift of manufacture. These data are usually stamped or printed indelibly on the lids of the metal containers.

Contact between metal containers and their contents often leads to undesirable chemical reactions, such as corrosion on the surface of the tin plate, or tin dissolved in the food product. These phenomena are seen most clearly in preserved foods that are highly acidic, such as marinades and vegetable appetizers. Marbling, or sulfide corrosion, usually forms in cans holding foods containing many protein substances (meat, fish, peas), because the tin or tin-plated iron reacts with the sulfur compounds of the protein products. This permanent bluish brown sulfide film is not harmful, but it detracts from the appearance of the food. In order to prevent corrosion and marbling, containers are made from prelacquered sheet metal (white tin, aluminum, aluminum alloys). Sometimes the finished containers are also spray-lacquered on the inside.

Since preserved foods are subjected to heat treatment (sterilization or pasteurization) and the microflora that might spoil the food is either absent or suppressed, such foods can usually be kept in ordinary storage places for long periods of time (usually for several years). The optimal storage conditions are a temperature between 0° and 20°C and a relative humidity not greater than 75 percent. In order to prevent their sugar from crystallizing, the temperature for preserves and jams should not be higher than 15°C.

Unsterilized preserved foods must be kept at low temperatures. The principal types of damage to the containers include bulging of the tops and bottoms of the containers from the gases formed by the vital activities of microorganisms (in cases of insufficient sterilization or by the reaction of the food acids with the metal of unvarnished cans); buckling; and rusting.

Veterinary and sanitary inspection of the preserved products determines their fitness as food. The ingredients permitted in preserved meat products include fresh meat, organ meats, and animal fats, all of which must undergo inspection. The contents of the cans are subjected to microbiological examination before sterilization. The goods are checked for taste, smell, and texture and tested in a laboratory to determine their physical, chemical, and microbiological properties. Only those canned goods are passed that satisfy sanitary requirements and the requirements of the All-Union State Standards.