Lactococcus lactis subsp. L. delbrueckii subsp. They also can cause rapid spoilage of milk because they are able to ferment lactose with the production of acid and gas, and are able to degrade milk proteins. They are killed by HTST treatment, therefore, their presence after treatment is indicative of contamination. Escherichia coli is an example belonging to this group.
Milk is potentially susceptible to contamination with pathogenic microorganisms.
Precautions must be taken to minimize this possibility and to destroy pathogens that may gain entrance Certain microorganisms produce chemical changes that are desirable in the production of dairy products such as cheese, yogurt. The microbial quality of raw milk is crucial for the production of quality dairy foods. Spoilage is a term used to describe the deterioration of a foods' texture, colour, odour or flavour to the point where it is unappetizing or unsuitable for human consumption. Microbial spoilage of food often involves the degradation of protein, carbohydrates, and fats by the microorganisms or their enzymes. In milk, the microorganisms that are principally involved in spoilage are psychrotrophic organisms.