Glutathione addition improves Oenococcus oeni adaptation to stress conditions of winemaking process

IVANA EMMERT; RAUL RAYA; PATRICIA CASTELLANO; LUCIA MENDOZA

Congreso; XII Congreso Argentino de Microbiología General SAMIGE 2017; 2017

During wine-making process after alcoholic fermentation can take place the malolactic fermentation (MLF). This secondary fermentation consists in the convertion of L-malic acid into L-lactic acid and it is an important step to obtain high quality wines. Oenococcus oeni is the best adapted species and is almost exclusively used as starter culture of MLF. However, viability and malolactic activity of O. oeni in wine depend on its resistance to several stress factors such as low pH and high concentrations of ethanol. Glutathione (GSH) is a non-proteic tripeptide that acts as an antioxidant and is considered a protective agent against adverse environments. The objective of this study was to investigate if glutathione addition can improve tolerance of O. oeni against stressful wine conditions. Two strains of O. oeni, X2L and Sb10, were cultured in MRS medium with and without GSH addition (5mM). These pre-cultures were sequentially inoculated in grape juice fermented by Saccharomyces cerevisiae mc2 containing L-malic acid (3 g/L). Bacterial growth was followed by viable cells counts and MLF was monitored using an enzymatic method. In addition, expression levels of mleA (malolactic enzyme), hsp18 (heat shock protein) and citE (citrate lyase) genes were evaluated by RT-qPCR. In presence of GSH, both strains of O. oeni showed higher biomass after 48 h of incubation being greater the GSH effect for the strain Sb10. During the sequential inoculation in fermented wines, O. oeni X2L and Sb10 showed higher viability and malolactic activity when were pre-adapted with GSH completing MFL at 4 days while cells pre-cultured without GSH were not able to remove of L-malic acid after 7 days. Moreover, in presence of GSH higher expression level of mleA gene was found in correlation to better MLF of O. oeni cultures pre-adapted with GSH. Genes involved in stress response, hsp18 and citE, also showed differential expression in pre-cultures grown with GSH. In conclusion the GSH addition had a positive effect on O. oeni growth during preparation of starter cultures and this previous adaptation step was able to improve the MLF performance of O. oeni when was inoculated in wines. These findings demonstrate the protective role of GSH against stressful conditions related to wine-making process.