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

Skim milk with low levels of added b-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 b-lactoglobulin and a-lactalbumin associated with the casein micelles increased with increasing b-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