Effect of Genetic Polymorphism on the Thermal Stability of β-Lactoglobulin and κ-Casein Mixture

Abstract

The effect of calcium chloride and genetic variants of κ-casein on the thermal stability of β-lactoglobulin isolated from bovine milk of known genetic types was investigated using differential scanning calorimetry. The effect of increasing calcium chloride from .10 to 1.0 M in piperazine-N,N’-bis(ethanesulfonic acid) buffer on the onset temperature, denaturation temperature, and width at half-peak height of these β-lactoglobulin was computed. β-Lactoglobulin BB was more stable than the other phenotypes at various β-lactoglobulin:κ-casein ratios in phosphate buffer. The stability of β-lactoglobulin was enhanced by the presence of κ-casein AA but lowered by κ-casein AB and BB. Data obtained from an equal mixture of β-lactoglobulin:κ-casein with various concentrations of calcium chloride also showed significant differences in thermal stability among the types of β-lactoglobulin and κ-caseins. Polymorphic combinations of β-lactoglobulin AB:κ-casein AA produced the most stable system to heat perturbation but those of β-lactoglobulin AA and κ-casein AA and β-lactoglobulin AA:κ-casein BB, the least. Our data also indicate that differences in width at half-peak height were associated with genetic polymorphism of these milk proteins.