Dr. Dharmakanta Kumbhakar
Milk is the best and most complete of all foods. It is secreted by the animals to serve as a sole and wholesome food for their suckling young ones. It is a fine blend of all the nutrients necessary for the growth and development of the young ones. The chief protein of milk is Casein – It occurs in combination with Calcium as Calcium Caseinogenate. The other proteins are Lactalbumin and Lactoglobulin. Animal milk contains nearly three times as much protein as human milk.
Milk proteins contain all the essential amino acids. The fat content of milk varies from 3.4 percent in human milk to 8.8 percent in buffalo milk. Human milk contains a higher percentage of Linoleic acid and Oleic acid than animal milk. Milk fat is a good source of Retinol and Vitamin D. The carbohydrate in all forms of milk is lactose or milk sugar. It is found nowhere else in nature. It is less sweet than cane sugar and is readily fermented by lactic acid bacilli. Human milk contains more sugar than animal milk. Milk contains almost all known minerals needed by the body such as Calcium, Phosphorus, Sodium, Potassium, Magnesium, Cobalt, Copper, Iodine, etc. Milk is particularly rich in Calcium; it is, however, a poor source of iron. Milk is a good source of all vitamins except Vitamin C. Thus, milk is a good source of proteins, fats, carbohydrates, vitamins, and minerals.
Though milk is the best and most complete of all foods, it must be clean and safe. Unsafe milk is an efficient vehicle for a great variety of disease agents. The source of infection or contamination of milk may be the dairy animal, human handler or the environment (e.g. contaminated vessels, polluted water, flies, dust, etc.). The infections of dairy animals that can be transmitted to human beings through milk are tuberculosis, brucellosis, streptococcal infections, staphylococcal enterotoxin poisoning, salmonellosis, Q fever, cow-pox, foot and mouth disease, anthrax, leptospirosis, and tick-borne encephalitis. The infections primary to humans that can be transmitted through milk are typhoid and paratyphoid fever, shigellosis, cholera, enteropathogenic Escherichia Coli and non-diarrhoeal diseases like streptococcal infections, staphylococcal food poisoning, diphtheria, tuberculosis, enterovirus, and viral hepatitis.
The first essential in the production of clean and safe milk is a healthy and clean dairy animal. Milk from a healthy udder contains only a few organisms, and these are relatively unimportant. Secondly, the premises where the animal is housed and milked should be sanitary. The milk vessels must be sterile and kept covered. The water supply must be bacteriologically safe. The milk handler must be free from communicable diseases, and before milking they must wash their hand and arms. Wherever possible, milking machines must be used. Milk should be cooled immediately to below 10 deg. C centigrade after it is drawn to retard bacterial growth. In the production of good quality milk, cleanliness of all containers and equipment in which milk is handled is very important.
Pasteurization is a preventive measure of public health importance and corresponds in all respects to the modern principles of supplying safe milk. Pasteurization may be defined as the heating of milk to such temperatures and for such periods of time as are required to destroy any pathogens that may be present while causing minimal changes in the composition, flavor and nutritive value. There are several methods of pasteurization. Three are mostly used:
- Holder (Vat) method: In this process, milk is kept at 63-66 deg. C for at least 30 minutes, and then quickly cooled to 5 deg. C. Vat method is recommended for small and rural communities.
- HTST method: In this 'high temperature and short time' method, milk is rapidly heated to a temperature of nearly 72 deg. C, and is held at that temperature for not less than 15 seconds and is then rapidly cooled to 4 deg. C. This is now the most widely used method as very large quantities of milk per hour can be pasteurized by this method.
- UHT method: In this 'ultra-high temperature' method, milk is rapidly heated usually in two stages to 125 deg. C for a few seconds only. It is then rapidly cooled and bottled as quickly as possible.
Pasteurization kills nearly 90 percent of the bacteria in the milk, including the more heat-resistant Tubercle Bacillus and the Q fever organisms. But it will not kill Thermoduric bacteria nor the bacterial spores. Therefore, despite pasteurization, with a subsequent rise in temperature, the bacteria are bound to multiply. In order to check the growth of micro-organism, pasteurized milk is rapidly cooled to 4 deg. C. It should be kept cold until it reaches the consumer.
Hygienically produced pasteurized milk has a keeping quality of not more than 8 to 12 hours at a temperature of 18 degrees.