Monitoring the effect of wine polyphenols on the growth of oenological yeasts

Abstract

Alcoholic fermentation is the main process in winemaking and yeasts are the responsible microorganisms. Polyphenols are major components of red grapes and they account for wine colour, taste and astringency, and they possess a remarkable antioxidant activity. The aim of this work was monitoring the effect of red grape polyphenol extracts on the growth of oenological yeasts by the microtiter plate assay and the multimode microplate reader Tecan Spark 10M. This is the first comparative study of the effect of grape polyphenols on the growth of non-Saccharomyces oenological yeasts. Oenological yeast strains of the following species were studied: Saccharomyces cerevisiae, Brettanomyces bruxellensis, Trigonopsis variabilis, Pichia holstii and Candida ishiwadae. Polyphenols extracts were obtained from red grape skins of the Vitis vinifera L. Cv. Tempranillo (TG) and Graciano (GG) cultivated in the northern Spanish region of Rioja. The effect of the polyphenol extracts on yeast growth was studied in the absence and in the presence of subinhibitory concentrations of ethanol. Our results showed different growth responses depending on the yeast species. Polyphenol extract concentrations higher than that naturally found in wines (3.12 g/L) showed an inhibitory effect on the growth of all the studied yeast strains. On the contrary, extract concentrations equal and lower than 3.12 g/L showed growth activation of S. cerevisiae and B. bruxellensis strains under both conditions of presence and absence of ethanol. Similarly, extract concentrations from 3.12 g/L showed growth activation of T. variabilis and P. holstii strains in absence of ethanol, whereas in the presence of ethanol only the TG extract showed growth activation and a protective effect against the antimicrobial effect of ethanol. Finally, in the case of C. ishiwadae TG and GG polyphenol extracts at the concentration of 3.12 g/L showed inhibitory effects on the yeast growth, both in presence and in absence of ethanol. In summary, for those yeast species particularly adapted to survive in a highly stressing medium such as red wine, their growth was favoured by the presence of polyphenols at the concentrations currently found in red grape musts and wines.