STUDY OF BETA-GLUCOSIDASE PRODUCTION BY WINE-RELATED YEASTS DURING ALCOHOLIC FERMENTATION. A NEW RAPID FLUORIMETRIC METHOD TO DETERMINE ENZYMATIC ACTIVITY

Aims: The b-glucosidase activity is involved in the hydrolysis of several important compounds for the development of varietal wine flavour. The aim of the present study was to investigate the production of b-glucosidase in a number of wine-related yeast strains and to measure and identify this activity over the course of grape juice fermentation. Methods and Results: b-glucosidase activity was measured as the amount of 4-methylumbelliferone released from 4-methylumbelliferyl-b-D-glucopyranoside substrate. Intact cells of some grape and wine-spoilage yeasts showed b-glucosidase activity much higher than those observed in wine yeasts sensu stricto. During fermentation, three Saccharomyces cerevisiae strains, one Hanseniaspora valbyensis strain and one Brettanomyces anomalus strain showed b-glucosidase activity both intra- and extracellularly. Conclusions: In the studied strains, b-glucosidase activity was at its maximum when the cells were in the active growth phase. However, a lowering of medium pH to values around 3 during fermentation led to total loss of activity. Significance and Impact of the Study: During the course of this study, a new, rapid and reproducible method to assay b-glucosidase activity was developed. The fact that Saccharomyces and non-Saccharomyces yeast strains are able to express b-glucosidase activity during the alcoholic fermentation sheds new light on the contribution of these yeasts in the aroma expression of wines.