Validation of a Standard Protocol to Assess the Fermentative and Chemical Properties of Saccharomyces cerevisiae Wine Strains

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.