Effect of genetic polymorphism on the thermal stability β-Lactoglobulin and K-Casein mixture

Abstract

The effect of calcium chloride and genetic variants of K-casein on the thermal stability of P-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-lactoglobu-lins was computed. β-Lactoglobulin BB was more stable than the other pheno-types at various β-lactoglobulin:K-casein ratios in phosphate buffer. The stability of β-lactoglobulin was enhanced by the presence of K-casein AA but lowered by K-casein AB and BB. Data obtained from an equal mixture of pMactoglobulin.-K-casein with various concentrations of calcium chloride also showed significant differences in thermal stability among the types of β-lactoglobulin and K-caseins. Polymorphic combinations of β-lactoglobulin BB:K-casein AA and β-lactoglobulin AB:x-casein AA produced the most stable system to heat perturbation but those of β-lactoglobulin AA and K-casein AA and β-lactoglobulin AA:K-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. © 2012 American Dairy Science Association.