UV-C treatment of grape must: Microbial inactivation, toxicological considerations and influence on chemical and sensory properties of white wine

UV-C was investigated to inactivate microorganisms in grape must. The aim was to evaluate the effect of UV-C on wine-related yeasts under winery conditions, to investigate the toxicological potential and to analyze the effects on chemical and sensory wine properties. Metschnikowia pukherritna showed the highest UV-C tolerance, Saccharomyces cerevisiae the lowest. With an initial cell count of 10(6) cfu/mL, M. pukherrima required a UV-C dose of > 1.2 kJ/L, S. cerevisiae < 0.8 kJ/L for inactivation. Inactivation efficacy decreased with higher must turbidity (26.7-144.5 NTU), optical density and degree of microbial load (10(4)-10(8) cfu/mL) suggesting a shadowing effect of individual microbes. UV-C treatment did not impact mutagenicity as tested by the Ames test. A decrease in dissolved oxygen and caftaric acid content indicated oxidative reactions. UV-C induced color bleaching (AE: 0-13) was also observed indicating a degradation of colored pigments. GC x GC-MS analysis revealed a decrease of 13-damascenone and linalool content in wines made from UV-C treated must. Descriptive analysis by a trained sensory panel showed that off-flavors did not occur at doses that were relevant for microbial inactivation (between 1.0 and 3.0 kJ/L). Industrial relevance: UV-C treatment is a non-thermal processing technique for the preservation of food. In this study, the applicability of UV-C treatment for the inactivation of spoilage yeast in grape must was demonstrated in pilot scale. The treatment provided sufficient microbial inactivation without having toxicological impact as examined by the Ames test and without causing off-flavor formation in the wines using relevant doses.