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

The effect of calcium chloride and genetic variants of K -C W ~~ on the thermal stability of fi-lactoglobulin isolated from bovine milk of known genetic types was investigated using differential scanning calorimetq. The effect of increasing calcium chloride from .10 to 1.0 M in piperazine-N,N'-bis(ethanesu1fonic acid) buffer on the onset temperature, denaturation temperature, and width at half-peak height of these fi-lactoglobuwas more stable than the other phenotypes at various f i -l a c t ~g l ~b d h : ~-~i ~e i n ratios in phosphate buffer. The stability of fi-lactoglobulin was enhanced by the presence of K-casein AA but lowered by ~c a ~e i n AB and BB. D a t a obtained from casein with various concentrations of calcium chloride also showed signiscant differences in thermal stability among the types of fi-lactoglobulin and Kcaseins. Polymorphic combinations of ptoglobulin AB:~-casein AA produced the most stable system to heat perturbation ~~I I S W ~S c~mputed ~-LactoglObulin BB an q u a l mixture Of $-lactoglobulin:Klactoglobulin BB:rt-~a~ein AA and &lacbut those of &lactoglobulin AA and Kcasein AA a d $-lactoglobulin AAXcasein BB, the least, Out data also mdicate that differences m width at halfpeak height were associated with genetic polymolphism of these milk proteins.