2. Milk proteins

2.1 Protein phase characteristics

Milk contains two groups of nitrogenous substances: proteins and non-protein nitrogenous substances (NPS), which account for 95% and 5% of milk nitrogen respectively:

• PNA varies from 3.1 to 7% of total nitrogen, with urea being the main component;

• Proteins differ from PNA in the size of their molecules, built up by complex assemblies of amino acids with molar masses ranging from 12 to 380 kDa. They are present in two different phases: on the one hand, an acid-unstable micellar phase, made up of solid particles in suspension known as casein micelles, and on the other, a stable soluble phase made up of various hydrophilic protein polymers, known as soluble proteins or serum...