No abstract

Eight wine yeast strains of Saccharomyces sp. were tested for polygalacturonase (PGase) activity, after cultivation on various carbon sources. No strain showed any activity when grown on glucose, while five strains produced PGase in the presence of galactose and polygalacturonate. These data suggest that the PGase of wine strains is repressed by glucose and induced by galactose and polygalacturonate. The existence of the PGase gene in the wine strains and its similarity with that of the laboratory strains was proved by Southern hybridization and PCR amplification. The promoter region of the PGase gene in the wine strains was slightly different from that of the laboratory strains. This possibly explains the different pattern of gene expression in wine and laboratory strains. The PGase of wine strains produced di- or tri-galacturonic acid from polygalacturonic acid, different from the fungal PGase.

Wines by yeast mutants producing polygalacturonase in high glucose concentration, from Saccharomyces wine-making strains, had higher filterability and more concentrated anthocyanin contents than that of their parent strains. These results suggest that the clarification process was improved at a lower cost by the low viscosity and that high-quality wines result from the increase in the anthocyanin contents.