Understanding the Contribution of Co-Fermenting Non-Saccharomyces and Saccharomyces Yeasts to Aroma Precursor Degradation and Formation of Sensory Profiles in Wine Using a Model System

Abstract

Comprehensive yeast strain characterization is an important issue for the wine industry as market demands require controlled production of distinctive high-quality wines. Glycosides form an important reservoir of varietal grape wine aroma, and their hydrolysis into olfactory-active compounds essentially depends on the fermenting yeast genera and strains. Among the 14 Metschnikowia, Pichia, Torulaspora and 18 Saccharomyces spp., rapid screenings by agar plate and activity assay, including the substrates arbutin, cellobiose and p-nitrophenol-β-D-glucopyranoside, revealed the most glycosidase-active strains. In the novel co-fermentation setups, five selected non-Saccharomyces and a Saccharomyces strain were separated by a 14 kDa cut-off membrane, allowing respective viable cell counts but facilitating metabolite transfer. Chemical analysis focused on aroma glycosides, with extensive quantification by GC-MS with SIDA on the extracted and hydrolyzed compounds. Olfactory profiles obtained for the non-Saccharomyces wines demonstrated a significant impact of these yeasts, albeit mainly correlated with increased hydrolysis of monoterpene glycosides, and surpassed by a technical Aspergillus niger enzyme. While screenings of non-Saccharomyces strains indicated enhanced glucosidase activity under winemaking conditions, their effect was lower than expected and dominated by ester formation. Interestingly, Saccharomyces yeast cell vitality was increased via in co-fermentation, and non-Saccharomyces strains displayed extended viabilities with high ethanol tolerances.