Cheese

Cheese, a food product made from milk. To obtain cheese, milk is subjected to coagulation—the process of curdling milk proteins; the resulting mass is processed by grinding, molding, pressing, etc., then the mass is left to ripen. The ripening of cheese consists of changes and decomposition of its components—casein, fat, as well as milk sugar—under the influence of microorganisms: part of the proteins first goes into a soluble state, and then, as the cheese ripens, decomposes with the formation of amino acids and other protein breakdown products; fat is partially broken down into free fatty acids, from which volatile acids (butyric and others) can give cheese a specific sharp odor; milk sugar turns into lactic acid, which forms salt-like compounds with organic bases, as well as with calcium, while partially, undergoing further decomposition, can form volatile propionic and acetic acids; due to the formation of volatile and gaseous decomposition products (carbon dioxide, etc.), holes—"eyes"—appear in cheese during ripening. Depending on the quality of milk, method of obtaining and processing the curd, and ripening conditions, taste characteristics are produced that characterize one or another variety of cheese. Two main groups of cheeses are distinguished: rennet cheeses, obtained from milk curdled with the help of rennet powder—a preparation containing rennet enzyme (see Chymosin), and sour milk cheeses, obtained from milk curdled with the help of lactic acid bacteria; by fat content, cheeses are divided into lean with fat content in the dry residue not more than 25%, semi-fat with 25-35%, fatty 35-45%, and creamy-more than 45%; depending on consistency, cheeses are divided into soft and hard; by type of milk, cow, sheep, and goat cheeses are distinguished. Sometimes to obtain a richer cheese, margarine is added to skim milk in the form of an emulsion; the product obtained is called "margarine cheese" and is inferior in taste to the real thing. In Japan and China, "vegetable cheese" is common, made from soybean curd (tofu).- The chemical composition of cheeses of Russian production - see Food products. In nutritional value and digestibility, cheese is close to meat. Of all dairy products, cheeses have the greatest storage stability; the most favorable storage temperature is 11-16° with relative air humidity of 85-90%. During storage, parasites often appear on cheese: 1) cheese mites (Acarus siro, Acarus longior), multiplying in old, long-unwashed cheeses, especially in warm and dry rooms; 2) larvae of the cheese fly (Piophila casei), more dangerous because when they infest cheese, they can penetrate deeply into it. Cheeses infested in this way cannot be freed from larvae that have penetrated deep inside and should not be allowed for consumption, since fly larvae are not indifferent to humans (see Myiasis). Spoilage of cheese can be accompanied by various phenomena: swelling, caused by abnormal fermentation under the influence of Bact. lactis aerogenes, B. coli commune, B. putrifucus, etc.; spreading—cheese becomes soft and loses its shape due to too rapid a ripening process; cracks—with too low humidity in the storage room; appearance of abnormal color—blue, red, etc.—from the development of various pigment-forming microorganisms; appearance of bitter, soapy taste, etc. All these defects, when they appear to a significant extent, serve as a basis for rejecting cheese. Toxins can be contained in cheese and cause poisoning phenomena (see Food infections, poisonings). Soft young cheeses, as well as overripe cheeses, more often cause poisonings than hard and well-aged ones. According to Miller, in diseases after cheese consumption, bacteria of the Salmonella group are often found, which forces consideration of the possible presence of these microbes when examining for pathogenic microbes. Pathogenic microbes can get into cheese from milk, from contaminated bacterial cultures used in cheesemaking, etc. Tubercle bacilli can remain viable from 14 to 104 days in various varieties of cheese when the latter are contaminated during manufacture. In this regard, Gotschlich^% expresses the opinion that in practice the danger of infections is small, since most cheeses are released for consumption 4 months after their manufacture. Typhoid bacilli retain viability for up to 12 days in various cheeses made from infected milk (Bitthorn); according to his data, when various cheeses are directly contaminated, viability is retained for 20-30 days. Miller points out that in cheese Bact. dysenteriae lives for 9 days, and V. cholerae asiaticae for 1 day. Regarding the causative agent of brucellosis—see Malta fever. According to Zdrodovsky, "brinza", made from goat and sheep milk, can be a cause of brucellosis.

Main preventive measures: 1) strengthening veterinary-sanitary supervision of dairy cattle and milk delivered for cheesemaking, 2) disinfection of milk (if possible) for the types of cheese being made by pasteurization, and 3) release of cheese for consumption only after satisfactory ripening, aged for a sufficiently long time, more or less ensuring the bactericidal action of cheese on pathogenic microflora (typhoid fever, brucellosis, etc.).- When studying the chemical composition of cheese for the purpose of determining nutritional value, it is customary to determine the amount of water, fat, and proteins; an idea of the degree of ripening can be given by the relationship between the amount of total N, amino acid, and ammoniacal N. When studying freshness, in view of the lack of developed objective methods, they are limited to organoleptic characteristics according to the variety of cheese. When falsification is detected, attention is paid to the nature of the fat, determining the constants in the fat extracted from the cheese under examination (see Butter, butter cow's), and examining for the content of chalk, gypsum, etc. Among harmful factors, attention is paid to heavy metals (Pb, Cu, Zn, etc.), to the toxin "cheese poison" (tyrosine), which is extracted with ether from an alkaline cheese extract, the ether is evaporated and the residue is subjected to a biological test on animals. Pathogenic microbes causing infections or forming toxins and causing poisoning are examined by the usual methods accepted in bacteriological technique.