WINE FERMENTATION METABOLITES PRODUCED BY TWO TORULASPORA DELBRUECKII STRAINS ISOLATED FROM OKANAGAN VALLEY, BC, CANADA VINEYARDS

Wine aroma is influenced by various factors, from agricultural practices in the vineyard to the enological choices made by winemakers throughout the vinification process. Spontaneous fermentations have a characteristically deeper complexity of aromas when compared to fermentations that have been inoculated with Saccharomyces (S.) cerevisiae because of the diversity of microflora naturally present on grape skins. Non-Saccharomyces yeast are being extensively studied for their ability to positively contribute to wine aroma and flavour. These yeasts are known to liberate more bound volatile compounds present in grape must than S. cerevisiae through the enzymatic action of β-glucosidases and β-lyases¹. Torulaspora (T.) delbrueckii is known to stand out among these nonconventional yeasts by increasing the content of esters, terpenes and thiols in wine fermentations, together with low production of acetic acid, hydrogen sulfide and acetaldehyde.

In a previous study using Pinot Noir grapes from the Okanagan Valley (BC, Canada)², a collection of non-Saccharomyces yeasts was isolated from late-stage spontaneous lab fermentations. These yeasts were screened for their fermentative performance based on residual sugar, ethanol concentration and production of non-volatiles such as glycerol and acetic acid in single fermentations using Chardonnay juice. From these, two strains of T. delbrueckii were selected for further analysis. The aim of the present work was to examine oenological traits such as ethanol, sulfite, and copper sulfate resistance for the two T. delbrueckii Okanagan Valley strains, the T. delbrueckii reference strain CBS1146, the commercial T. delbrueckii strain Zymaflore Alpha and a control S. cerevisiae strain. These five strains were also used to perform single yeast fermentations in Muscat juice. Non-volatile compounds were quantified by HPLC/RID and analyzed by ANOVA with no significant differences in residual sugars, ethanol and glycerol production, while CBS1146 displayed lower acetic acid than the other 4 strains. Volatiles such as terpenes, primary alcohols and esters were also semi-quantified by SPME-GC/MS, followed by Partial Least Squares-Discriminant Analysis. Differences were observed among the strains in aroma compounds including limonene, γ-terpinene, α-terpineol, ocimene, phenylethyl alcohol and 2-phenethyl acetate. This work will add to developing research on T. delbrueckii from the perspective of BC and Canadian wines.