conservation of foodstuff

From Big Medical Encyclopedia

CONSERVATION of foodstuff (Latin conservare to store, keep) — the processing of foodstuff protecting them from damage and ensuring long safety.

At To. the methods providing death of microorganisms, or transferring them to a condition of anabiosis are used. Under influence To. also activity of enzymes of microorganisms is suppressed. To. allows to create stocks of perishable foodstuff (see) to move them on a long distance regardless of climatic conditions and to provide the necessary range of food stuffs for all year.

Technical progress in technology K. allowed to implement in practice the methods providing high stability of food stuffs at long-term storage with preservation their food, flavoring and biol, properties.

Classification of methods K. it is presented in the table.

Table. Classification of methods of conservation of foodstuff

The thermal method is used most widely. This method K. it is based on dying off of different types of microorganisms under the influence of temperature influence. Vegetative forms of microorganisms are generally inactivated at t ° 60 — 70 ° within 1 — 10 min., except for the thermophilic bacteria capable to survive at t 80 °. Disputes which inactivation requires heating higher than 100 ° on exposure of 30 min. till 2 — 3 o'clock differ in resistance to high temperature.

Sterilization (see) provides release of the preserved foodstuff from vegetative forms of microorganisms and from a dispute. At sterilization the modes with t ° 108 — 120 ° within 40 — 90 min. are used.

To. liquid foodstuff — milk, vegetable and fruit juice, beer — it is made pasteurization (see). At the same time foodstuff is exempted from viable pathogenic microorganisms of intestinal group, mycobacteria of tuberculosis and some other microorganisms. Distinguish low pasteurization, edges it is carried out at t ° 65 ° within 20 min., and high — at t ° 85 — 90e within no more than 1 min. At the same time the sufficient effect with the minimum change of food and flavoring properties, the pasteurized products is provided.

Low temperature is the best preserving factor providing preservation of perishable foodstuff with the smallest changes of natural properties and the smallest losses of biologically active components of food — vitamins, enzymes, etc. Under the influence of low temperature (— 20 ° below) the majority of microorganisms stops the development, except for psikhrofil, fungi and a mold which keep viability at t ° — 20 ° below. The low temperature applied at To., does not kill microorganisms but only stops their growth. Such pathogenic microorganisms as salmonellas and staphylococcus, survive in the frozen foodstuff within several months.

To. by low temperature it is made by cooling of foodstuff or its freezing. Cooling represents impact of low temperature on foodstuff with finishing temperature in the thickness of it from 4 to 0 °. During the cooling foodstuff, without being exposed to freezing, keeps food, flavoring and biol, properties. Most often To. cooling meat is exposed. The X wound of the cooled products is made in refrigerators at t ° from 0 to 2 ° and it is not higher than 85% of relative humidity. The cooled meat can be stored without signs of damage to 20 days.

the Diagrammatic representation of microdrugs of muscular tissue at various speed of freezing: and — fabric of fresh-killed meat (it is given for comparison); — very quickly frozen (in the drawing a large number of small crystals of ice is visible); in — slowly frozen (crystals of ice are larger); — very slowly frozen (big crystals of ice are visible). Crystals of ice are specified by shooters.

Freezing significantly breaks structure of cells and fabrics of the frozen products which after thawing differ from fresh products markedly (fig., a). At slow freezing in cells of the preserved foodstuff large crystals of ice (fig., in, d) which destroy covers and cellular elements are formed. In the course of thawing water is not returned to colloids and the product is exposed to dehydration; at the same time proteic and other nutrients are lost. Helps to keep high quality of products during the thawing a way of snap-freezing. In this case a large number of small crystals is formed (fig., b); at their thawing water easily is returned to colloids of which they were formed. Snap-freezing gives the minimum losses of vitamins and provides the smallest development of microorganisms in products.

Quality of the frozen products depends on a way of thawing. Bystry thawing of the frozen meat is followed by considerable losses of nutritious, extractive and biologically active agents. Therefore the frozen meat should be thawed slowly.

Dehydration (drying) — To., based on the termination of life activity of microorganisms at foodstuff moisture content less than 15%. At To. drying microorganisms do not perish, and pass into a condition of anabiosis; during the moistening of a product they become viable again. Drying with a usual atmospheric pressure can be natural and artificial. Solar drying (receiving dry fruit) and jerking belong to methods of atmospheric drying (for long preservation of fish products).

Artificial stack drying can be jet, raspylitelny and film. At a jet method drying is made in drying chambers in which foodstuff is exposed to continuous jet action of the hot air arriving from heaters; moisture is removed through special vent systems.

The Raspylitelny drying used for dehydration of liquid foodstuff (milk, eggs, tomato juice), is made in the special camera at t ° 90 — 150 ° by spraying of a liquid product through a nozzle in a slick, edges under the influence of a hot air quickly dries and in the form of powder settles on a bottom of the camera. At raspylitelny drying the product is exposed to short-term action of high temperature in this connection it changes a little and keeps all the natural properties. The dry products (powders) received thus at addition of water easily are recovered in the initial product suitable for the use.

To. liquid products it can be made also by method of film drying by means of drawing a liquid product on the heated surface of the rotating reel. The products received by method of film drying considerably concede to the products made by raspylitelny drying. So, solubility of milk powder from raspylitelny drying reaches 97 — 99% whereas powdered milk of film drying is dissolved only for 80 — 85%.

The vacuum drying made usually at a low temperature ensures full safety of foodstuff. One of types of vacuum drying is lyophilizing (see). Philosophy of lyophilizing as method K. dehydration of a product in the conditions of vacuum and removal of moisture directly from crystals of ice is, passing a liquid phase. In the course of lyophilizing distinguish three periods. In the first period the products loaded into a sublimator are affected by a high vacuum, at Krom the product samozamorazhivatsya and directly from crystals of ice there is an evaporation of moisture. In the dried-up products temperature reaches — 17 °. This period lasts 15 — 25 min. during which is removed apprx. 18% of moisture. In the second period at t ° — 10 — 20 ° is removed apprx. 80% of moisture, then plates on which the dried-up products are located heat. At the same time products are not defrozen and removal of moisture continues directly from crystals of ice. Drying in the second period continues 10 — 20 hours depending on humidity and the weight of a product. In the third period thermal vacuum drying at t is made ° 45 — 50 ° within 3 — 4 hour.

The pickles and conservation are made by sugar on the basis of increase in osmotic pressure. This method K. it is based on property of microorganisms to keep viability only on condition of a certain difference of osmotic pressure in a bacterial cell and the environment (osmotic pressure in a bacterial cell is slightly higher, than in the environment). Increase in osmotic pressure in foodstuff leads to disturbance of exchange between a microbic cell and external environment, to dehydration of a cell, reduction of volume of protoplasm and death of a microbic cell. Solutions of sodium chloride and sugar differ in high osmotic pressure. So, the osmotic pressure of 1% of solution of sodium chloride or sugar is equal to 6,1 atm.

At To. the pickles applies 8 — 12% solutions of sodium chloride that corresponds to 50 — 73 atm of osmotic pressure, a cut provides a reliable conserving effect. However there are microorganisms (Serratia salinaria) capable to maintain high concentration of sodium chloride (to 15 — 20%). Dry, wet, warm and cold saltings are in practice used. At a dry salting the salted products are processed by dry salt, without brine. Wet, or tuzluchny, the salting is made by immersion of a product in in advance prepared saturated salt solution. The ambassador of the frozen products is called cold, and the ambassador at a temperature of an ambient air — warm. To. the nek-swarm is followed by nutritive loss a pickles.

At To. sugar usually creates its concentration apprx. 60% that corresponds to 350 atm of osmotic pressure. So high pressure provides a reliable conserving effect — storage during a long term at any ambient temperature.

Pickling and a fermentation are based on ability of microorganisms to develop in narrow limits of pH. Change of the size pH breaks dispersion of protoplasm of a microbic cell and stops its life activity. So, at pH lower than 4,5 life activity of putrefactive bacteria stops (change of concentration of hydrogen ions in practice is carried out by method of pickling). During the pickling are used food to - you, including acetic to - that, edges in concentration of 4 — 6% are caused by death of microorganisms, and in concentration of 1 — 1,8% weakens life activity of microorganisms and transfers them to a condition of anabiosis. For increase in efficiency To. pickling is combined with pasteurization and a pickles. Marinated products shall be stored at a temperature not over 6 °.

At a fermentation change of concentration of hydrogen ions is combined with specific action milk to - you are sugar it is fermented in milk to - that. Under the influence of a fermentation life activity of pathogenic not sporiferous microflora completely is suppressed and there is an inactivation of eggs of helminths.

Conservation by means of antiseptic agents and antibiotics. Chemical preservatives at To. foodstuff in our country are applied restrictedly; only some chemical substances in quantities, not unhealthy consumers are allowed. As chemical preservatives food antiseptic agents (the benzoic, sulphurous and sorbic to - you), antibiotics and antioxidants are used. The benzoic to - that in the quantities applied to preservation is harmless, however its preserving properties are small. Certainly admissible daily dose of the benzoic to - you to 5 mg/kg and conditionally admissible dose of 5 — 10 mg/kg of body weight. In the USSR the benzoic to - that is allowed in fruit jelly, a fruit candy, jam and in melange in number of 700 mg/kg; in preserves (sprat) and fruit juices — 1000 mg/kg. Sulphurous to - that, sulphurous anhydride, sodium bisulphate and sodium pyrosulphate are applied to sulphitation of fruits and vegetables. Under the influence of sulphitation the best keeping of products and higher content in them ascorbic to - you is provided. The sulphited vegetables and fruits in the course of thermal treatment are exposed to partial desulphitation. Contents sulphurous to - you in fruit juice and dry fruit is allowed to 100 mg/kg, in a tomato puree — to 1500 mg/kg. Sorbic to - that is most acceptable for To. foodstuff. It is characterized by high antimicrobic action and the smallest manifestation of any negative effects on an organism. Transformation sorbic to - you in an organism happens as transformations unsaturated fat to - t. Certainly admissible daily dose sorbic to - you — to 12,5 mg/kg, conditionally admissible dose — 12,5 — 25 mg/kg of body weight. Sorbic to - that is allowed in soft drinks in number of 300 — 500 mg/kg, in fruit juices and condensed milk — 1000 mg/kg, at surface processing of cheeses — 2000 mg/kg, and half-smoked sausages — 5000 mg/kg.

Antibiotics for the purposes K. are applied in extremely limited assortment and volume. In the food industry only such antibiotics which are not applied in medicine for are allowed to lay down. are more whole also which along with high antimicrobic action are unstable in the environment and are inactivated at thermal treatment. By way of exception in the food industry biomycin — only in the form of biomitsinovy ice is used (5 g of tetracycline on 1 t of ice). Biomitsinovy ice is used in transit on a long distance of fish of cod breeds and meat. Use of chlortetracyclin of a hydrochloride for To. food stuffs in our country are not allowed. In the USSR use of two antibiotics — nystatin and chlortetracyclin of a hydrochloride for processing of meat hulks by irrigation by their solutions is temporarily authorized (chlortetracyclin a hydrochloride — 100 mg and nystatin — 200 mg on 1 l of water). To processing of some vegetable and fruit products it is applied lowlands, are especially sensitive to Krom staphylococcus. Nizin has ability to reduce stability a dispute to heating that promotes their more effective inactivation. Antioxidants are applied to the prevention of damage of fats. As antioxidants of fats butyl hydroxyanisol, buthylhydroxytoluene and dodecyl gallate are allowed. As antioxidants of fats it can be used ascorbic to - that and ascorbyl palmitate.

Smoking and prezervirovaniye treat the combined methods K. Action on a product of the smoke having the preserving properties is the cornerstone of smoking. Smoking smoke contains the complex of sublimates showing antiseptic action. Among products of smoking smoke there are pitches and some substances carried to cancerogenic. Due to the cancerogenic danger in sovr, conditions smoke smoking is replaced with use of smoking liquid, free from the substances having cancerogenic properties. Smoking includes a complex of impacts on foodstuff — a pickles, drying, heating. Distinguish hot (t ° 80 — 140 ° during several hours) and cold (at t ° not higher than 40 °) smoking. These types of smoking are applied by hl. obr. at To. fishes. Smoke-cured fish treats perishable goods, the term of her storage shall not exceed the 72nd hour. Subject to cold smoking previously salted fish.

Prezervirovaniye represents a complex of the influences ensuring safety of products in a sealed container without signs of damage within several months. As the preserving factors at the same time pickling, a pickles and pasteurization are used. Storage of preserves shall be made at t ° 6 — 8 °.

Has Nek-ry prospects To. ionizing radiation. This method is comprehensively studied in many countries of the world.

See also Canning production , Canned food .

Bibliography: Hygiene of food, under the editorship of. K. S. Petrovsky, t. 1, M., 1971; L about An about in D. I. Production technology of products of public catering, M., 1967; Petrovsky K. S. Gigiyena of food, M., 1975; Merchandizing of foodstuff, under the editorship of F. V. Tserevitinov, t. 2, 4, M., 1949.

K. S. Petrovsky.