Abstract
Different Saccharomyces cerevisiae strains are simultaneously or in succession involved in spontaneous wine fermentations. In general, few strains occur at percentages higher than 50% of the total yeast isolates (predominant strains), while a variable number of other strains are present at percentages much lower (secondary strains). Since S. cerevisiae strains participating in alcoholic fermentations may differently affect the chemical and sensory qualities of resulting wines, it is of great importance to assess whether the predominant strains possess a “dominant character.” Therefore, the aim of this study was to investigate whether the predominance of some S. cerevisiae strains results from a better adaptation capability (fitness advantage) to the main stress factors of oenological interest: ethanol and temperature. Predominant and secondary S. cerevisiae strains from different wineries were used to evaluate the individual effect of increasing ethanol concentrations (0-3-5 and 7% v/v) as well as the combined effects of different ethanol concentrations (0-3-5 and 7% v/v) at different temperature (25–30 and 35°C) on yeast growth. For all the assays, the lag phase period, the maximum specific growth rate (μmax) and the maximum cell densities were estimated. In addition, the fitness advantage between the predominant and secondary strains was calculated. The findings pointed out that all the predominant strains showed significantly higher μmax and/or lower lag phase values at all tested conditions. Hence, S. cerevisiae strains that occur at higher percentages in spontaneous alcoholic fermentations are more competitive, possibly because of their higher capability to fit the progressively changing environmental conditions in terms of ethanol concentrations and temperature.
Highlights
Spontaneous grape juice fermentation into wine is carried out by the yeast populations naturally occurring on the grape surface and in the winery environment (Sabate et al, 2002; Bisson, 2012)
Considering that temperature and ethanol during alcoholic fermentation are held responsible for the ability of S. cerevisiae to dominate on non-Saccharomyces yeasts or on other Saccharomyces spp. (Goddard, 2008; Williams et al, 2015; Alonso del-Real et al, 2017; Henriques et al, 2018), the adaptability to these two factors could be involved in determining the dominance of predominant on secondary S. cerevisiae strains
When the yeast population reached the maximum growth yield, 637 isolates belonging to S. cerevisiae species were analyzed by mitochondrial DNA restriction analysis
Summary
Spontaneous grape juice fermentation into wine is carried out by the yeast populations naturally occurring on the grape surface and in the winery environment (Sabate et al, 2002; Bisson, 2012) In this process, in the vats filled at the beginning of the vintage, non-Saccharomyces yeast species usually predominate in the early stages and later, with ethanol increasing, they are replaced by Saccharomyces cerevisiae because of higher resistance of this yeast species to alcohol (Pretorius, 2000; Bisson, 2005; Querol and Fleet, 2006; Albergaria and Arneborg, 2016). The predominance of S. cerevisiae strains with particular resistance capability to these two stress factors could contribute to the construction of an ecological niche typical of each fermentation tank and possibly winery
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