κ-Casein—β-Lactoglobulin Interaction in Solution When Heated

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Summary Heating a mixture (0.5% of each) of β -lactoglobulin and κ -casein at pH 7 at 90C 15min led to interaction between the two proteins. Electrophoresis at pH 2.1 showed that, before heating, the components moved independently; whereas, after heating, a single component of intermediate mobility was observed. Ultracentrifuge examination of the heated mixture showed a new component with an S 20 value of 45, three times greater than the S 20 value of κ -casein. The ability of the κ -casein to stabilize calcium-sensitive casein was considerably reduced in the heated mixture. The clotting time of κ -casein by rennin was increased by the addition of β -lactoglobulin and was increased still further when the mixture had been heated. The clot formed by the action of rennin on the heated mixture contained the β -lactoglobulin as well as the κ -casein.