Possible sources of contamination during production, storage and processing including:
*Inflammation of udder
*Animal itself: skin of teats and udder
*Condition at the milking area
*The milking operator
*Utensils and equipment used during processing
*The air and environment
Contamination occurs when microorganisms enter into the milk. The control of microbial activity in milk and milk products, especially the control of bacterial and bacterial growth, is the most important function in the handling and manufacturer of dairy products.
Raw milk, when improperly handled, may undergo any of several adverse changes. It may become sour due to the growth of bacteria that produce lactic acid.
Some bacteria, especially coliforms, ferment milk and produce gas. Clostridium butyricum, Candida pseudotropicalis and Torulopsis sphaerica are some of the organisms which produce gas in milk while fermenting the lactose.
Raw milk may also be subject to peptonisation (digestion of casein), the formation of rope (viscous polymer of sugars), and sweet curding, when bacterial growth is not controlled.
Enterobacter aerogenes, Micrococcus spp. Streptococcus spp. etc cause ‘ropy milk’. They cause the milk to become viscous or stringy, and produce a gummy substance in the medium.
Dairy herds are tested for tuberculosis and tested for and vaccination for brucellosis, and most milk is pasteurized to prevent the transmission of a variety of food –borne disease. However, some pathogens may be survive the pasteurization process, possibly because they may be protected by fat in which they may become encapsulated.
Research shows that 70-90% of raw milk samples tested contained psychotropic bacteria capable of producing proteinases that were active after heating at 149 °C for 10s.
Grams positive psychotropic bacteria also can produce lipases in milk which is associated the development of rancid flavor in UHT milk.