Natural Proteolysis in Whey and Susceptibility of Whey Proteins to Acidic Proteases of Rennet

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Abstract
Whey protein concentrates vary considerably in solubility and in heat stability of the protein. The possibility was determined that rennet whey undergoes natural proteolytic changes which may be responsible for these differences. Endopeptidase activity in rennet wheys from cheese factories and rennet wheys prepared in the laboratory was negligible. The casein digestion test indicated that neutral or alkaline proteases were absent. Hemoglobin digestion at acidic pH indicates trace amounts of acidic proteases, most likely derived from the rennet. No changes were detected by gel filtration on Sephadex G-75 and by polyacrylamide gel electrophoresis with sodium dodecyl sulfate in the protein pattern upon aging wheys for a few days. The albumin band of laboratory whey diminished during storage at pH 4. Individual whey proteins were incubated at pH 6.2 and 4.5 with high concentrations of commercial rennet. .alpha.-Lactalbumin and .beta.-lactoglobulin were not affected. At pH 4.5 serum albumin was degraded extensively, and the H-chain of the immunoglobulins underwent limited digestion.

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