Great epidemic role of milk as it can be a source of infection with tuberculosis, anthrax, brucellosis, foot and mouth disease, toxoplasmosis, Q fever and other infectious diseases dangerous to humans. It is extremely dangerous to human milk, cows, sheep, goats, patients with mastitis (udder inflammation). It contains a purulent release of iron, which are found in large quantities staphylococci and streptococci, which cause food poisoning. Pathogens in milk are not only from infected animals, but also through sick people, bacilli carrier, from the environment. In milk, they find favorable conditions for its development, and multiply, can cause the spread of infectious diseases, since lactic acid bacteria able to completely suppress their livelihoods. Activators of typhoid and paratyphoid can maintain their livelihoods in the milk of more than 20 days.

Particularly long survival and multiplies rapidly in the milk of dysentery Sonne bacillus. Tubercle bacillus coxpanyaet their livelihoods in the milk of 10 days in milk products – 20 days in cheeses – 2 years. Activators of brucellosis in milk live 10-40 days, milk products – 15, in butter – 30 days. Sanitary requirements for milk quality. When evaluating the sanitary quality of milk are guided by its organoleptic characteristics, acidity, chemical composition and degree of contamination.

These standards are shown in the GOST 13264-70 "milk cow. Requirements for the blanks. " Reductase assay is an indirect indicator of bacterial contamination of milk. The more microorganisms in the milk, the more active the enzyme. There are two tests for reductase: with methylene blue, with rezazurinom. Reductase assay with rezazurinom less time consuming. The results of the reactions is determined by the disappearance of color. In the first version with methylene blue results are browsing in 20 minutes, 2 and 5.5 hours in the second – after 20 minutes and 1 hour Rezazurin under the reductase recovery goes through several stages, which have different colors. Color change indicates the number of this enzyme and the extent of contamination. Initially, there is a blue-steel color. Under the action of the enzyme is reduced to rezazurin rezarufina, which stains the milk pink. Formed from rezarufina degidrorezarufin – milk bleached. If after 20 minutes in vitro appears white color, milk is assessed as very poor (fourth grade). If after 1 h of milk paint turns pink or white, milk, referred to as third class. If the stain with the blue-violet, it is believed that milk is the second class. If the milk is 1 h does not change its color, it belongs to the first class. Class of bacterial contamination of milk is determined by GOST 9225-84 "Milk and dairy products. Methods for microbiological analysis. " – Bada – Supplement the diet of man in minerals, vitamins and trace elements.