Abstract
This paper reports on a common experiment performed by 17 Research Units of the Italian Group of Microbiology of Vine and Wine (GMVV), which belongs to the Scientific Society SIMTREA, with the aim to validate a protocol for the characterization of wine strains of Saccharomyces cerevisiae. For this purpose, two commercial S. cerevisiae strains (EC 1118 and AWRI796) were used to carry out inter-laboratory-scale comparative fermentations using both synthetic medium and grape musts and applying the same protocol to obtain reproducible, replicable, and statistically valid results. Ethanol yield, production of acetic acid, glycerol, higher alcohols, and other volatile compounds were assessed. Moreover, the Fourier transform infrared spectroscopy was also applied to define the metabolomic fingerprint of yeast cells from each experimental trial. Data were standardized as unit of compounds or yield per gram of sugar (glucose and fructose) consumed throughout fermentation, and analyzed through parametric and non-parametric tests, and multivariate approaches (cluster analysis, two-way joining, and principal component analysis). The results of experiments carried out by using synthetic must showed that it was possible to gain comparable results from three different laboratories by using the same strains. Then, the use of the standardized protocol on different grape musts allowed pointing out the goodness and the reproducibility of the method; it showed the main traits of the two yeast strains and allowed reducing variability amongst independent batches (biological replicates) to acceptable levels. In conclusion, the findings of this collaborative study contributed to the validation of a protocol in a specific synthetic medium and in grape must and showed how data should be treated to gain reproducible and robust results, which could allow direct comparison of the experimental data obtained during the characterization of wine yeasts carried out by different research laboratories.
Highlights
Saccharomyces cerevisiae is the predominant yeast species in winemaking
Due to its adaptability to the stressful conditions imposed by grape must fermentation, it competes with other yeasts and bacteria, and being the main actor of the transformation of grape must into wine, it is universally known as the “wine yeast.”
The microbial assemblages correlate with specific climatic features, and this suggests a link between vineyard environmental conditions and microbial residence patterns. These findings reveal the importance of microbial populations for the regional identity of wine (Bokulich et al, 2016) and underline that the utilization of S. cerevisiae indigenous strain with selected traits is fundamental to modulate the final characteristics of the wine
Summary
A wide number of molecular and physiological studies demonstrated the high genotypic and phenotypic diversity of S. cerevisiae wine strains (Romano et al, 2008; Csoma et al, 2010; Mercado et al, 2011; Capece et al, 2013; Tristezza et al, 2013; Legras et al, 2018; Peter et al, 2018) This biodiversity is strictly associated with a significant high technological variability (Pretorius, 2000) and is of great importance for a successful strain selection and the development of new starters able to modulate the organoleptic quality of wine (Romano et al, 2003). Wine fermentations using native wild strains obtained from oaks produce earthy and sulfurous organoleptic characteristics but intense of citrus and floral attributes (Hyma et al, 2011)
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