Answer:
The milk of goats and sheep is similar in composition to that of cows.
Milk protein consists mainly of casein, and it exists in several classes: α, β, etc. If milk pH falls below 4.6, the casein precipitates. Although casein represents 80–85% of total milk protein, when precipitation occurs, the liquid portion is referred to as whey.
The remaining proteins are found in whey, and they include serum albumin, immunoglobulins, α-lactalbumin, etc. Milk carbohydrate is lactose, and its content is fairly consistent among breeds of milk cows at around 5.0%.
lactose is the main sugar; smaller quantities of glucose and citric acid exist. The fat content varies between ca. 3.5 and 5.0% depending upon cattle breed.
The ash content of around 0.7% consists of a relatively high level of Ca2+ and a lower level of Fe2+.
The pH of fresh whole milk is around 6.6 but it may reach ca. 6.8 from a cow that has mastitis.
Mastitis is an infection of the udder that is most often caused by Streptococcus agalactiae and S. Uberois but sometimes by Staphylococcus aureus or Streptococcus dysgalactiae.
Fresh milk of mastitis cows mainly has leucocytes (white blood cells) >106/ml as compared to nonmetastatic milk which has 70,000/ml leucocytes.
Milk contains a very adequate supply of B vitamins with pantothenic acid and riboflavin being the two most abundant. Vitamins A and D are added for human consumption, and their presence has no known effect on the activity of microorganisms.
Overall, the chemical composition of whole cow’s milk makes it an ideal growth medium for heterotrophic microorganisms, including the nutritionally fastidious Gram-positive lactic acid bacteria. However, the milk microbiota utilizes these constituents and brings about its spoilage.
