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pH and Protein Instability*

Wine proteins are derived primarily from grapes and autolyzed yeast. They consist of several (protein) fractions which appear to be the subunits of denatured grape enzymes. Their molecular weight varies from 20,000 to 40,000 Daltons. The polypeptides with molecular weights of less than 10,000 are mostly derived from yeast autolysis. The isoelectric point (PI) of wine protein fractions have been reported to be in the range of 2.5 - 8.7.