YEAST DERIVATIVE PRODUCTS: CHARACTERIZATION AND IMPACT ON RIBOFLAVIN RELEASE DURING THE ALCOHOLIC FERMENTATION

Abstract

Light-struck taste (LST) is a wine fault that can occur in white and sparkling wines when exposed to light. This defect is mainly associated to the formation of methanethiol and dimethyl disulfide due to light-induced reactions involving riboflavin (RF) and methionine [1]. The presence of RF in wine is mainly due to the metabolism of yeast [2] which fermenting activity can be favoured by using yeast derivative products (YDPs) as nutrients. Nonetheless, a previous study showed the addition of YDPs before the alcoholic fermentation (AF) led to higher concentrations of RF in wines [3]. Due to the widespread use of YDPs in the winemaking process, this study aimed to understand the possible relation between the content of RF in wine and the YDP adopted as nutrient for AF.

The experimental plan included (i) the characterization of selected YDPs and (ii) their addition as nutrient in microvinification trials using must as medium. Fourteen commercial YDPs of different nature (inactivated yeasts [IYs], mannoproteins [MPs], yeast autolysates [YAs], yeast extract [YEs] and yeast hulls [YHs]) were chosen. They were characterized in terms of flavins (RF, FAD and FMN), amino acid profile and sulfur-containing compounds (e.g. reduced glutathione [GSH], cysteine, cell wall cysteine and adsorbed cysteine). The characterized IYs, YEs and YHs were used for fermentation trials, carried out in Chardonnay must with 4 Saccharomyces cerevisiae strains. Flavins were quantified before and after the alcoholic fermentation.

Both YEs and one YA were the richest in RF which increase up to 20 μg/L was estimated considering an addition in must of 40 g/hL. These YDPs showed also the highest concentration of amino acids (up to 300 mg/L). However, among the flavins, FMN was the major one in most of the analyzed YDPs. With regards to GSH, this tripeptide was found at the highest concentration in the same YA (13.2 mg/g). The addition of YDPs caused a variation in RF released during AF depending on both the yeast strain and YDP nature. The addition of YEs caused an RF increase in must of about 15-20 μg/L, in accordance to RF content found in these products. For one of the yeast strains investigated, RF fatherly increased up to 30 μg/L during AF.

These results evidence the impact of YDPs on RF content indicating that the selection of nutrients combined with the choice of fermenting yeast strain should be considered for preventing the risk of LST appearance.