Selection of wine yeasts and malolactic bacteria for desirable glycosidases and sensory enhancement of wines
Abstract
Selection of wine yeasts and malolactic bacteria for desirable glycosidases and sensory enhancement of wines
Summary
This report summarises research activities in the selection of wine yeasts and malolactic bacteria for desirable beta-glycosidase activity and sensory enhancement of wines.
Glycosidase activity of wine yeasts and wine bacteria was found to be principally due to β-glucosidase. Some α-arabinosidase and α-rhamnosidase activity was also detected but this was relatively minor compared to the activity of β-glucosidase. A series of wine microorganisms (87 yeast and 105 bacterial strains) were screened for β-glucosidase activity using a β-glucoside analogue (4-methylumbelliferyl-β-D-glucopyranoside) incorporated into agar plates. This method gave a visual indication of β-glucosidase activity. The majority of the organisms tested exhibited some β-glucosidase activity.
The agar plate method using 4-methylumbelliferyl-β-D-glucopyranoside as a substrate only provides a qualitative estimation of β-glucosidase activity. A quantitative assay using the β-glucoside analogue, ρ-nitrophenyl-β-D-glucopyranoside, (pNPG) was therefore developed in liquid culture. Lactic acid bacteria generally had higher activities of β-glucosidase than the wine yeasts examined although the fastidious nutritional requirements of lactic acid bacteria prevented direct comparisons to be made.
β-glucosidase activity was found to be pH dependent, with little activity below a pH of 3.0 and maximum activity between pH 3.5 and 4.0. β-Glucosidase activity of all the wine yeasts screened with the exception of Saccharomyces cerevisiae was affected by ethanol in the incubation medium. Glucose in the incubation medium inhibited the expression of β-glucosidase activity in all of the organisms studied. This effect was particularly evident in cultures of Saccharomyces cerevisiae.
Grape glycosides were purified from grape juice by passage down a C18 column and added to a chemically defined grape juice medium. Fermentations were then carried out and the glycosidase activity of wine yeasts assessed by determining the decrease in the glycosyl-glucose content of the juice using the GG assay. H. anomala and S cerevisiae had the greatest glycosidase activity in this medium, followed by K. apiculata. C. pulcherima had the weakest glucosidase activity. Differences in glycosidase activity may have the potential to be exploited by the wine industry for the release of flavour and aroma compounds of wine that are glycosidically bound. The potential to use these non-S. cerevisiae enzymes-systems in wine production techniques requires further investigation.