Characteristics of Yeast Polygalacturonases Induced during Fermentation on Grape Skins

Polygalacturonase activity in must prepared from Muscat Bailey A (Bailey x Muscat Hamburg) grapes increased markedly at one day after the addition of yeast, whereas no enzyme activity was detected throughout fermentation in must made from the juice alone. Polygalacturonase activity increased in musts made using either fresh or heated skins. These results indicated that polygalacturonase was produced by growing yeasts and that the skin fraction (skins and seeds) was necessary for production of the enzyme. Three polygalacturonases (PG-I, II, and III) were separated from the skin fraction by DEAE Sepharose Fast Flow column chromatography. PG-I released a monomer, dimer, and trimer from the substrate polygalacturonic acid, whereas PG-II and III released only the monomer. The optimal pH of both PG-I and II was 3.5, whereas that of PG-III was 4.5. The activities of PG-I, II, and III were partially inhibited by SO 2 and ethanol.