The effect of temperature and time of heating whole milk on the renninclotting time, the primary phase of rennin action and the protein (mainly β-lactoglobulin) soluble in 2% trichloroacetic acid (TCA), have been studied. Considerable changes in these parameters occurred above 60°C. The primary phase was inhibited (the degree of inhibition being both temperature and time-dependent), the clotting time was increased, and the protein soluble in 2% TCA decreased considerably.
It is suggested that the inhibition of the primary phase was due to complex formation between κ-casein and β-lactoglobulin, the increase in clotting time to a combination of complex formation and a change in the distribution of Ca, and the decrease in β-lactoglobulin to both its interaction with κ-casein and its heat denaturation. The relevance of such changes to the heat stability of milk is discussed.
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