High pressure-induced denaturation of (alpha)-lactalbumin and (beta)-lactoglobulin in bovine milk and whey: a possible mechanism

In this study, high pressure (HP)-induced denaturation of (alpha)-lactalbumin ((alpha)-la) and (beta)-lactoglobulin ((beta)-lg) in dairy systems was examined. In both milk and whey, (beta)-lg was less baroresistant than (alpha)-la; both proteins were considerably more resistant to HP-induced denaturation in whey than in milk. HP-induced denaturation of (alpha)-la and (beta)-lg increased with increasing proportion of milk in mixtures of milk and whey. Addition of a sulphydryl-oxidising agent, KIO3, to milk or whey increased HP-induced denaturation of (beta)-lg, but reduced the denaturation of (alpha)-la. Denaturation of both (alpha)-la and (beta)-lg was prevented by adding a sulphydryl-blocking agent, N-ethylmaleimide, to milk or whey prior to HP treatment, highlighting the crucial role of sulphydryl-disulphide interchange reactions in HP-induced denaturation of (alpha)-la and (beta)-lg. Removal of colloidal calcium phosphate from milk also reduced HP-induced denaturation of (alpha)-la and (beta)-lg significantly. The higher level of HP-induced denaturation of (alpha)-la and (beta)-lg in milk than in whey may be the result of the abscence of the casein micelles and colloidal calcium phosphate from whey, which facilitate HP-induced denaturation of (alpha)-la and (beta)-lg in milk.