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To evaluate the capacity of Oenococcus oeni strains to release aroma compounds from glycosylated precursors by measuring glycosidase activities with both synthetic and natural substrates. Five glycosidase activities were investigated in 47 O. oeni strains using synthetic substrates. This screening revealed that activity levels vary considerably, not only for each strain (depending on the substrate tested), but also between strains. Fifteen strains exhibiting different activity profiles were further analysed using natural substrates extracted from both untoasted and toasted oak. In the latter, various amounts of aromatic compounds were measured, thus confirming the specific potentials of the selected strains, but the results were different from those obtained using synthetic substrates. In addition, the use of toasted wood extracts significantly increased the release of wood aromas, which minimized differences between strains. The capability of O. oeni to hydrolysate glycoconjugate aroma precursors is strain-dependent and variable, depending on the substrate. Instead of synthetic substrates, natural aroma precursors should be used for an adequate evaluation of the glycosidase potential of O. oeni. [ABSTRACT FROM AUTHOR]

Aims: Wine is the product of complex interactions between yeasts and bacteria in grape must. Amongst yeast populations, two groups can be distinguished. The first, named non- Saccharomyces (NS), colonizes, with many other micro-organisms, the surface of grape berries. In the past, NS yeasts were primarily considered as spoilage micro-organisms. However, recent studies have established a positive contribution of certain NS yeasts to wine quality. Amongst the group of NS yeasts, Brettanomyces bruxellensis, which is not prevalent on wine grapes, plays an important part in the evolution of wine aroma. Some of their secondary metabolites, namely volatile phenols, are responsible for wine spoilage. The other group contributing to wine aroma, which is also the main agent of alcoholic fermentation (AF), is composed of Saccharomyces species. The fermenting must is a complex microbial ecosystem where numerous yeast strains grow and die according to their adaptation to the medium. Yeast–yeast interactions occur during winemaking right from the onset of AF. The aim of this study was to describe the interactions between B. bruxellensis, other NS and Saccharomyces cerevisiae during laboratory and practical scale winemaking. Methods and Results: Molecular methods such as internal transcribed spacer-restriction fragment length polymorphism and polymerase chain reaction and denaturing gradient gel electrophoresis were used in laboratory scale experiments and cellar observations. The influence of different oenological practices, like the level of sulphiting at harvest time, cold maceration preceding AF, addition of commercial active dry yeasts on B. bruxellensis and other yeast interactions and their evolution during the initial stages of winemaking have been studied. Brettanomyces bruxellensis was the most adapted NS yeast at the beginning of AF, and towards the end of AF it appeared to be more resistant than S. cerevisiae to the conditions of increased alcohol and sugar limitation. Conclusions: Among all NS yeast species, B. bruxellensis is better adapted than other wild yeasts to resist in must and during AF. Moreover, B. bruxellensis appeared to be more tolerant to ethanol stress than S. cerevisiae and after AF B. bruxellensis was the main yeast species in wine. Significance and Impact of the study: Brettanomyces bruxellensis interacts with other yeast species and adapts to the wine medium as the dominant yeast species at the end of AF. Contamination of B. bruxellensis might take place at the beginning of malolactic fermentation, which is a critical stage in winemaking. [ABSTRACT FROM AUTHOR]