Survey of Yeast Acid Proteases for Effectiveness of Wine Haze Reduction

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Abstract
Eight yeast strains were identified consistently exhibiting proteolytic activity in model wine solutions, having activities ranging from 0.05 to 0.28 µmol of glycine equivalents per mL per minute at pH 3.3. The activity of the crude protease suspensions decayed with time, showing different decay responses depending upon the organism tested. Protease activity was maintained in actual wine solutions, but at somewhat reduced levels. Proteolytic activity was correlated with reduction in protein-induced haze in wine. Using a protease preparation from Kloeckera apiculata, analysis by high pressure liquid chromatography of wine protein content following incubation of the protease concentrate with Chenin blanc and Chardonnay wines showed the degradation of wine proteins. Inhibitor studies on the Kloeckera protease suspension indicated that the proteolytic activity is completely inhibited by EDTA, pepstatin, and, α-2-macroglobulin, suggesting that the protease (or proteases) is an acid endopeptidase requiring a metal ion either for activity or proper protein conformation.

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