The water solubility of proteins refers to the force of interaction between proteins and water, mainly the interaction that occurs between the side chains of peptide bonds in proteins and water molecules. Different proteins have different peptide bond side chains and different water solubility.
The water solubility of proteins is not only related to their own chemical structure, but also affected by solvent pH, ionic strength, temperature and other factors.
According to solubility, proteins can be categorized into clear proteins (serum proteins, ovalbumin, α-lactalbumin), globulins (β-lactoglobulin), alcohol-soluble proteins, and glutenins.
Specifically, clear proteins are soluble in water at pH 6.6, globulins are soluble in water at pH 7, alcohol-soluble proteins are insoluble in water but soluble in 70% ethanol, and glutenins are insoluble in water and alcohols but soluble in strong acid and base solutions.