Identification of riboflavin low producer yeasts to prevent the light-struck taste in white wines
AIM: Wine quality maintenance during the storage is a fundamental aspect for both wine producers and consumers. Nowadays, great attention has been given to the light effect, causing detrimental changes of wine; indeed, light can induce off-flavours associated to the light-struck taste (LST)(1). This fault is due to photochemical oxidation processes in which riboflavin (RF) and methionine (Met) play an important role generating methanethiol (MeSH) and dimethyl disulphide (DMDS)(2), responsible of the unpleasant cabbage and onion-like odours that make wine undrinkable. Although it is well-known the contribution of yeasts in the final amount of these compounds in wine, microbiological strategies against the LTS defect limiting their release are not yet available. This study is part of the project “Innovative and sustainable approaches for the prevention of photo-induced defects in white wines and sparkling wines (Enofotoshield)” and in particular it aims at providing wineries with alternative microbiological approaches to counteract the LST.
METHODS: Four Saccharomyces cerevisiae strains of oenological interest (EC1118, IOC18, LS2 and AWRI796) have been compared to investigate the RF release during their growth in synthetic media (SMY and SMV) and Chardonnay must, simulating oenological conditions. Then, the RF release (including the derived flavones) was estimated by UPLC (Ultra-Performance Liquid Chromatography) analysis.
RESULTS: Results of this study revealed that RF production is influenced by the growth medium composition. Indeed, if the medium contains RF, the vitamin concentration increases over time while that of flavones remain constant; on the contrary, the opposite situation is verified in absence of RF. Moreover, investigations on other factors that could influence the RF release are still in progress (such as cell inoculum density, temperature, oxygen-limiting conditions, availability of nutrients). Taking in consideration that a lower concentration than 80-100 μg/L could limit the LST development, the best identified condition in terms of RF release was the growth on the Chardonnay must (12,8 μg/L) compared to the two synthetic media SMY and SMV (102,4 μg/L and 316,5 μg/L, respectively).
This study paves the way for the development of new approaches that limit the impact on the wine aromatic profile. Indeed, the choice of the growth cultural medium is a relevant factor in terms of RF and Met production. The next steps of the study will be the analysis of the Met release and of the intracellular content of both RF and Met.
Issue: Macrowine 2021
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wine microbiology, light-struck taste, yeasts