Abstract
The inoculation of wines with autochthonous yeast allows obtaining complex wines with a peculiar microbial footprint characteristic from a wine region. Mixed inoculation of non-Saccharomyces yeasts and S. cerevisiae is of interest for the wine industry for technological and sensory reasons. However, the interactions between these yeasts are not well understood, especially those regarding the availability of nutrients. The aim of the present study was to analyze the effect of nitrogen and sugar concentration on the evolution of mixed yeast populations on controlled laboratory-scale fermentations monitored by density, plate culturing, PCR-DGGE and sugar and nitrogen consumption. Furthermore, the effect of the time of inoculation of Saccharomyces cerevisiae respect the initial co-inoculation of three non-Saccharomyces yeasts was evaluated over the evolution of fermentation. Our results have shown that S. cerevisiae inoculation during the first 48 h conferred a stabilizing effect over the fermentations with non-Saccharomyces strains tested and, generally, reduced yeast diversity at the end of the fermentation. On the other hand, nitrogen limitation increased the time of fermentation and also the proportion of non-Saccharomyces yeasts at mid and final fermentation. High sugar concentration resulted in different proportions of the inoculated yeast depending on the time of S. cerevisiae inoculation. This work emphasizes the importance of the concentration of nutrients on the evolution of mixed fermentations and points to the optimal conditions for a stable fermentation in which the inoculated yeasts survived until the end.
Highlights
Wine is the result of alcoholic fermentation performed by yeasts during a complex process that transform the sugars present in the grape must into ethanol and carbon dioxide
It has been previously described that nitrogen concentration below 140 mg/L are limiting to growth and result in a decrease of the fermentation rate by S. cerevisiae, an increase the risk of sluggish and stuck fermentation as well as an increase in residual sugars (Bell and Henschcke, 2005; Martínez-Moreno et al, 2012; Tesnière et al, 2015)
This could be explained by the different nitrogen requirements of the selected S. cerevisiae strain, autochthonous yeast that was grown in YPD before its inoculation in the synthetic must, allowing inner nitrogen accumulation
Summary
Wine is the result of alcoholic fermentation performed by yeasts during a complex process that transform the sugars present in the grape must into ethanol and carbon dioxide. During this alcoholic fermentation, a microbiological population evolves as a consequence of the chemical changes produced in the environment (Riberéau-Gayon et al, 2006). With the aim to obtain wines that reflect a certain terroir, a previous study part of the WILDWINE project (Mas et al, 2016) accomplished the isolation and the characterization of multiple yeast strains from Priorat region to better understand the winemaking process and to determine the source of microorganisms that produce a particular microbial footprint (Padilla et al, 2016b). Non-Saccharomyces yeasts are able to produce metabolites or hydrolyze aromatic precursors providing new wine styles and enhancing their complexity (Ciani et al, 2010; Viana et al, 2011; Andorrà et al, 2012; Jolly et al, 2014)
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