Bioprotective effect of a Torulaspora delbrueckii/Lachancea thermotolerans mixed inoculum and its impact on wines made.

Abstract

SO2 is an additive widely used as antimicrobial in winemaking industry. However, this compound can negatively affect health, so the search for alternatives is currently a line of research of great interest. One of the proposed alternatives to SO2 as an antimicrobial is the use of bioprotection yeasts, which colonize the medium preventing the proliferation of undesirable microorganisms. 

In this work, the bioprotective effect of a mixed inoculum formed by Torulaspora delbrueckii/Lachancea thermotolerans (70/30) during fermentation was evaluated. In order to compare the effect of the studied inoculum with that exerted by SO2 or the inoculation of other commercial yeasts, four different fermentation strategies were tested: spontaneous fermentation, spontaneous fermentation sulfited, fermentation with the mixed inoculum and fermentation with a commercial Saccharomyces cerevisiae yeast. In the first three strategies, after 72 hours the commercial S. cerevisiae yeast was inoculated in order to ensure complete fermentations. Populations of yeasts, lactic bacteria and acetic bacteria, and the physical-chemical parameters of the wines were studied.

The different fermentation strategies caused a differentiation in the yeast species present during fermentation and in the diversity of species found. Regarding populations of lactic acid and acetic acid bacteria, results showed that the effect of the addition of the mixed inoculum reduced the presence of these microorganisms to levels similar to those found in sulfited vinifications.

The analysis of the wines obtained showed differences in some parameters such as lactic acid, which was higher in wines fermented with the mixed inoculum. This result is related to the presence of L. thermotolerans in the mixed inoculum. The high concentration of lactic acid also resulted in higher total acidity in wines fermented with the mixed inoculum. In the color parameters, the wines made with the mixed inoculum together with those inoculated at vatting with S. cerevisiae showed a higher anthocyanin ionization index compared to the wines made by spontaneous fermentation.

The results obtained indicate that the use of the T. delbrueckii/L. thermotolerans mixed inoculum studied can exert a bioprotective effect comparable to that of SO2 in controlling
populations of lactic acid bacteria and acetic acid bacteria during fermentation. In addition, it causes an increase in the acidity of the wine through the production of lactic acid, result of great interest to combat the effects of climate change, and improves some parameters related to color, such as the anthocyanin ionization index.

This study has been co-funded (50/50) by the European Regional Development Fund (ERDF) and the Government of La Rioja, within the ERDF operational program of La Rioja 2014-2020.