β-Glucosidase Activity andbglGene Expression ofOenococcus oeniStrains in Model Media and Cabernet Sauvignon Wine

Strains of Oenococcus oeni performing malolactic fermentation might prove an interesting source of β-glucosidase enzymes, which can release aromatic volatile compounds from their flavorless glycoconjugate precursors present in wine. Many studies have been conducted using strains cultured in winelike media, but little is known about the activity of these strains in real wine. In this work, real Cabernet Sauvignon red wine was used as the culture medium to test β-glucosidase activity and bgl gene expression of four O. oeni strains. Assays in wine were compared with winelike medium and mixtures of wine and MRS broth medium. β-Glucosidase activity was detected in both whole-cell and supernatant fractions for all four strains tested, although results varied depending on the conditions. The highest activity was found in wine (4 U/mg) and the activity was inhibited in the presence of fructose. To measure bgl expression, the RNA of O. oeni was extracted directly from red wine for the first time. Using real-time qPCR, the relative expression of the bgl gene was evaluated. The expression of this gene varied depending on the strain and it was overexpressed in samples of wine diluted with MRS. These results could be of importance to the wine industry and in studies of strain adaptation to wine for the selection of starters.