The following points highlight the four mediums of contamination of milk by microorganisms. The mediums are: 1. The Dairy Cattle 2. The Milking Area 3. The Milking Equipment 4. Persons Handling Milk.
Medium # 1. The Dairy Cattle:
Milk contains microorganisms at the time of the its being drawn (milking) from the dairy cattle. A number of diseases like tuberculosis, brucellosis, fever, Streptococcus- and Staphylococcus- infections may be transmitted through milk to man.
These organisms are mechanically pushed out during milking. The number present at the time of milking has been reported between several hundred to several thousands per ml of milk.
Particles of manure, soil, etc. adhering to the skin of the udder and teats can gain entry into milk during milking causing contamination.
To avoid all these the health of the dairy cattle should be given due care and the udder and teats should be essentially cleaned properly before milking. The flanks of the animal should be clipped closely to minimise the chances of hair as well as adhering particles of dust which harbour bacteria from falling into milk during milking.
Medium # 2. The Milking Area:
The microbial content of the air is greatly affected by many conditions and practices. Accumulation of manure, dirt and throwing of hay in milking area adds to the microbial population of air. These airborne microorganisms may contaminate the milk. Air is generally considered to be a minor factor among the sources of contamination.
But, under certain conditions, it assumes great importance especially when wide mouth pails are used and outdoor milking is done in dusty yards without prior washing. Maintenance of clean area and minimization of activities that create dust certainly reduce the potential of contamination from this source.
Medium # 3. The Milking Equipment:
Use of unclean milking machines, milk cans, pipe lines, strainers, bulk tanks, and other equipment’s prove to be the most important source of milk contamination. Negligence in their proper cleaning before use affords ideal conditions for the growth of microorganisms.
The thermoduric and thermophilic bacteria surviving pasteurization multiply rapidly, contributing to high counts in the finished products. Therefore, it is very necessary that the milking equipment’s be thoroughly cleaned and effectively treated with bactericidal agents. High temperature (hot water or steam) or chlorine or quaternary ammonium compounds are commonly used as sanitizing agents.
Medium # 4. Persons Handling Milk:
Persons concerned with milking and handling of milk may also contaminate milk. Therefore, all persons involved in the milking process must be in good health and must follow procedures consistent with good sanitary techniques. Milkers must wash their hands properly, rinse them with some bactericidal solution and dry with clean towel before commencement of milking.
The possibility of diseased milkers contributing to pathogenic organisms is of great importance. Streptococcus spp. and Corynebacterium diphtheriae may be transmitted directly from the throat to the milk by coughing or sneezing. Dysentery bacilli may contaminate the milk through the hands of the person concerned.