Influence of hydrolysis temperature and pH on the selective hydrolysis of whey proteins by trypsin and potential recovery of native alpha-lactalbumin

Whey protein isolate (93.84% protein) was hydrolysed using bovine trypsin (EC 3.4.21.4) at an enzyme-to-substrate ratio of 1.0% (w w^-1) over a range of temperatures and pH. Residual protein was quantified using reversed-phase high performance liquid chromatography. Genetic variants A and B of β-lactoglobulin (β-Lg) and α-lactalbumin (α-La) showed higher resistance to trypsin hydrolysis at 25°C than at 50°C with higher susceptibility of β-LgA than of β-LgB. Under the conditions trialled, the highest (67.87%) residual pure α-La was at 25°C and pH 8.5 (2h hydrolysis; degree of hydrolysis 7.11%), while the lowest (7.99%) was at 50°C, pH 8.5 (5min). Above pH 7.5 and 40°C, β-Lg dimer-monomer transition occurred resulting in improved trypsin hydrolysis. Trypsin hydrolysis outside the optimum pH and temperature offers potential for selective removal of β-LgAnd production of pure and native α-La.