The protein interactions and rheological properties of skim milk heated in the presence of low levels of reducing agent

Abstract

Skim milk with low levels of added β-mercaptoethanol (SM−ME) and untreated skim milk (SM) were heated and then made into acid gels. Acid gels prepared from heated SM−ME had markedly higher firmness and contained more protein connections than acid gels prepared from heated SM. Electrophoretic analyses of the milks showed that the levels of β-lactoglobulin and α-lactalbumin associated with the casein micelles increased with increasing β-ME concentration. The levels of disulphide-linked whey proteins were higher in SM−ME than in SM. This suggested that there may be higher levels of initiators for thiol−disulphide exchange reactions, resulting in an increase in the rate of the reactions and the formation of greater numbers of small aggregates, in SM−ME than in SM. Consequently, acid gels made from SM−ME may have more bonds and more particles participating in the network, resulting in firmer gels, than acid gels made from SM.