A study on bovine kappa-casein aggregation after the enzymatic action of chymosin

Kappa-casein (κ-CN) is a milk phospho-glycoprotein that plays an important role in the electrostatic and steric stabilization of casein micelles suspensions. κ-CN characteristics such as its aminoacidic composition and its high denaturalization temperature make this protein an excellent nutrient. The enzymatic destabilization of κ-CN is the basis of cheese and yoghurt manufacture. In this paper, modifications on the κ-CN aggregation process by hydrolysis with chymosin derived from the initial protein state and the presence of sucrose and lactose were studied. Our study shows that, during its self-association, κ-CN opens its conformation by raising the exposition of hydrophobic regions to the medium. Hence, the initial polymerization or association state of κ-CN affects on the aggregation stage after the enzymatic action of chymosin. The inhibition of aggregation when the protein was previously associated suggests that the region which participates in the aggregation of p-κ-CN particles, would be the one involved in the self-association during the heating of κ-CN samples. Sucrose and lactose also affect the aggregation of proteolized particles of κ-CN. Furthermore, the nature and the concentration of the added sugars had significant influence on the protein aggregation process.