Evaluating the effect of oxygen addition on yeast physiology, population dynamics and wine chemical signature in controlled mixed starter fermentations

[摘要] ENGLISH SUMMARY: The use of commercial starter cultures of non-Saccharomyces yeast, usually together withSaccharomyces cerevisiae, has become a trend in the global wine industry in the past decade.Depending on the specific species of non-Saccharomyces yeast, the procedure may aim atenhancing aroma and flavour complexity of the wine, reduce acetic acid levels, and/or lower theethanol yield. However, the contribution of non-Saccharomyces yeast strains depends on severalfactors, and in particular on the strains ability to establish significant biomass and to persist for asufficient period of time in the fermentation ecosystem. For an effective use of these yeasts, it istherefore important to understand the environmental factors that modulate the population dynamicsof such environments. In this study, we evaluated the effect of oxygen addition on yeast physiology,population dynamics and wine chemical signature in controlled mixed starter fermentations. Thepopulation dynamic in co-fermentations of S. cerevisiae and three non-Saccharomyces yeastspecies namely, Torulaspora delbrueckii, Lachancea thermotolerans, and Metschnikowiapulcherrima, revealed that oxygen availability strongly influences the population dynamics andchemical profile of wine. However, results showed clear species-dependent differences. Further,experiments were confirmed in Chardonnay Grape juice, inoculated with L. thermotolerans and S.cerevisiae with different oxygen regimes. The results showed a trend similar to those obtained insynthetic grape juice, with a positive effect of oxygen on the relative performance of L.thermotolerans. The results in this study also indicates that continuous stirring supports the growthof L. thermotolerans.We further analysed the transcriptomic signature of L. thermotolerans and S. cerevisiae in singleand mixed species fermentations in aerobic and anaerobic conditions. The data suggest the natureof the metabolic interactions between the yeast species, and suggests that specific stress factorsare more prominent in mixed fermentations. Both yeasts showed higher transcript levels of geneswhose expression is likely linked to the competition for certain metabolites (copper, sulfur andthiamine), and for genes involved in cell wall integrity. Moreover, the transcriptomic data also alignedwith exo-metabolomic data of mixed fermentation by showing higher transcripts for genes involvedin the formation of aroma compounds found in increased concentration in the final wine.Furthermore, the comparative transcriptomics analysis of the response of the yeasts to oxygenprovides some insights into differences of the physiology of L. thermotolerans and S. cerevisiae. Alimited proteomic data set aligned well with the transcriptomic data and in particular confirmed ahigher abundance of proteins involved in central carbon metabolism and stress conditions in mixedfermentation. Overall, the results highlight the role of oxygen in regulating the succession of yeasts during winefermentations and its impact on yeasts physiology. The transcriptomics data clearly showedmetabolic interaction between both yeasts in such ecosystem and provide novel insights into theadaptive responses of L. thermotolerans and S. cerevisiae to oxygen availability and to the presenceof the other species.

[发布机构] Stellenbosch University