The protein content of milk is influenced significantly by the feeding and varies between 3.0 and 3.6%. For cheese making this has a special significance, as the yield in cheese making is controlled by the protein content.
The protein content of the milk is not uniform, but consists of two fractions, i.e., the casein and the whey proteins (serum proteins). These fractions can be further split into components and are different in chemical composition.
Milk proteins not only are important for the manufacturer of traditional dairy products but also have a multitude of functional characteristics and high nutritional values, e.g. casein is the major component of cheese and contributes its physical consistency to acidified products,. Individual specific protein fractions such as caseinate, whey protein concentrates or coprecipitates have wide significance in the spectrum of foods such as in infant formula and even some pharmaceutical products.
Casein, which is 80% of the milk protein, is arranged in milk in precisely formed micelle (clusters of individual molecules). Apart from casein, micelles contain a fairly high percentage of colloidal calcium phosphate. Within the range of normal technical processing conditions, they are stable when it comes to thermal and mechanical processing. The casein micelle is sensitive to changes in charge. When milk turns sour, structural change can be observed at PH <5.0, a gel is formed and minimal stability is reached.
The whey proteins are groups of compounds, called albumin and globulin. The thermal modenaturation of whey proteins plays a role, as it is linked with desirable and undesirable modifications:
- A firmer gel structure in acidified products, especially in yoghurt
- An improved water retention capability
- A reduced whey excretion with acidified gels
- Yield increase in fresh cheese products
- Cooked taste
- Soiling of surfaces in heat exchangers
- Reduced lab precipitation of milk
- Change of functional properties in milk powders
Proteins in Milk
