Impact of yeast derivative products of riboflavin and methionine synthesis during the alcoholic fermentation

Riboflavin (RF) and methionine (Met) are the main actors of the light-struck taste (LST), a defect occurring in white and rosé wines if exposed to light in the visible spectrum; LST is associated to the formation methanethiol and dimethyl disulfide, and the consequent development of unpleasant aroma described as onion, garlic and cooked cabbage. Every year, this fault causes high economic losses to wineries [1]. The presence of these undesired compounds in wines is mainly attributed to the metabolism of the fermenting yeasts. However, another source of these two precursors (RF and Met) could be the yeast derivative products (YDPs), used as nutrients. Since the use of YDPs as nutrients is a widespread practice in winemaking processes, this work aimed at investigating if selected YDPs could contribute both on the release of RF and Met in wine and on the increase of the expression of the genes involved in their biosynthetic pathways (RIB5 and MET6). In particular, six selected YDPs were added to a Chardonnay must at the concentration of 40 g/hL to perform alcoholic fermentation experiments using four Saccharomyces cerevisiae oenological starters (EC1118, IOC18-2007, LS2, AWRI796); results revealed that the addition of YDPs at the fermentations recorded a variation in terms of RF release, depending on the yeast strain and YDP nature. Two of the six tested YDPs (containing hulls and inactivated yeasts, respectively) were selected to perform a laboratory large-scale fermentation, since they showed a lowest impact on RF release during the alcoholic fermentations performed by the four starters. IOC18 and AWRI796 strains, showing the lowest and the highest RF release respectively, were investigated in order to evaluate the fermentative performance at different temperature (18°C and 25°C), the RF and Met release and also the expression of RIB5 and MET6 genes during the alcoholic fermentation by qPCR experiments.