Yeast selection criteria for improvement of sulphite management in winemaking

Sulphite is widely used in winemaking for its antimicrobial and antioxidant properties, although its toxic effect on human health is proven. The aim of this work is to be intended in the recent strong efforts to lower the levels of chemical preservatives in wine. Indeed, there is a general need to improve knowledge concerning yeast regulation of sulphite metabolism during fermentation, since this would give new guidelines for strain choice and for critical control of fermentation parameters, in order to maximize the effects of sulphite and to allow a lower addition during vinification. Accordingly, sulphite resistance mechanisms have been studied extensively in Saccharomyces cerevisiae. Wine yeasts can cope with SO2 by different systems. SO2 detoxification through the plasma membrane protein Ssu1p is one of the most efficient resistance mechanisms in S. cerevisiae (Avram & Bakalinsky, 1997; Park & Bakalinsky, 2000). Wine yeasts also cope with SO2 by means of other systems, such as acetaldehyde production and the upregulation of sulphite reduction systems or whole sulphur metabolism (Casalone et al., 1992). Furthermore, they usually produce by themselves SO2 in low to medium amounts, depending on the strain and on fermentation conditions. In this study, we investigated the behaviour towards sulphite of five commercial wine starters together with eight yeasts isolated during local selection projects. Among the latter group, 4 strains are also undergoing whole genome sequencing and transcriptome analysis during fermentation. These strains were isolated using novel selection criteria that take into account wine quality and health which have been introduced as selection criteria together with standard technological constraints.