Conditions limiting the influence of thiol–disulphide interchange reactions on the heat-induced aggregation kinetics of β-lactoglobulin

Abstract

The effects of calcium and N-ethylmaleimide addition on the heat-induced denaturation/aggregation of β-lactoglobulin at neutral pH were examined. Aggregation of unfolded β-lactoglobulin was found to be rate limiting on heating aqueous protein solutions, while stoichiometric additions of calcium indicated that the unfolding reaction was limiting. Increased binding of calcium reduced the zeta potential of β-lactoglobulin to a minimum of −5 mV, resulting in first-order denaturation/aggregation kinetics at pH 7.0. Thiol–disulphide interchange reactions had a positive effect on the aggregation of unfolded β-lactoglobulin at low protein concentrations and low ionic strength. In the presence of calcium, the absence of thiol–disulphide interchange reactions did not affect the protein aggregation kinetics. Thiol–disulphide interchange reactions had little effect on storage modulus development of heated β-lactoglobulin (3%, w/w) acid gels; however, they enhanced the strain stability. Results showed the importance of non-specific forces in controlling the heat-induced aggregation of unfolded β-lactoglobulin.