Shearing accelerates denaturation of β-lactoglobulin and α-lactalbumin in skim milk during heating

Abstract

Shearing is an embedded step during thermal processing of milk that can add additional impact on native proteins. Behaviour of native proteins in bovine skim milk was studied at different temperatures (70–100 °C) for 5 min with or without applying a constant shear rate at 1000 s−1. Shear stress generated generally decreased with increase in temperature due to decrease in milk viscosity which displayed a Newtonian fluid behaviour. β-Lactoglobulin (β-Lg) and α-lactalbumin (α-La) denatured rapidly even at low temperature (70 °C) under the shearing and about 25% more of them denatured at 85 °C than those of the non-sheared counterparts. Shearing predominantly induced formation of thiol/disulphide aggregates mainly consisting of β-Lg and α-La, as well other minor whey proteins and caseins. These results highlighted the necessity of assessing impact of shearing on milk proteins when optimising thermal processing conditions.