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

¹ Department of Animal Science, Macdonald Campus of McGill University, 21,111 Lakeshore Road, Ste. Anne de Bellevue, PQ, Canada H9X 1C0
² Food Research Centre, Agriculture Canada, Ottawa, ON, Canada K1A 0C6

The effect of calcium chloride and genetic variants of -casein on the thermal stability of ß-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 ß-lactoglobulin was computed. ß-Lactoglobulin BB was more stable than the other phenotypes at various ß-lactoglobulin:-casein ratios in phosphate buffer. The stability of ß-lactoglobulin was enhanced by the presence of -casein AA but lowered by -casein AB and BB. Data obtained from an equal mixture of ß-lactoglobulin:-casein with various concentrations of calcium chloride also showed significant differences in thermal stability among the types of ß-lactoglobulin and -caseins. Polymorphic combinations of ß-lactoglobulin AB:-casein AA produced the most stable system to heat perturbation but those of ß-lactoglobulin AA and -casein AA and ß-lactoglobulin AA:-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.

Key Words: genetic polymorphism ßbeta;-lactoglobulin • -casein • thermal stability

Submitted on August 16, 1990
Accepted on December 10, 1990