Abstract
Due to the greenhouse gas increase, grapes are often exposed to high temperatures in several growing areas especially during the final developmental stages, and this is particularly true when early ripening cultivars are harvested. This may cause undesirable effects on berry metabolism and composition and wine quality, particularly concerning the aroma profile. Harvesting at night or keeping the harvested grapes in cold rooms before vinification are empirical protocols applied in specific viticultural areas. To study the effects of decreasing berry temperature after harvest, white-skinned berries (cv Vermentino) were maintained at 4 or 10°C for 24 or 48 h before processing (pre-cooling). Control grapes were kept at 22°C. Grapes cooled at 10°C for 24 and 48 h resulted richer in polyphenols and showed a significant up-regulation of genes involved in polyphenols biosynthesis (i.e., VvPAL, VvSTS2, and VvFLS1). Similar behavior was observed in samples kept at 4°C for 48 h. Pre-cooling induced specific changes in the volatile organic compound (VOC) profiles. In particular, higher amounts of a specific subcategory of terpenes, namely sesquiterpenes, were detected in cooled samples. The induction of the expression of key genes involved in terpenoids biosynthesis (VvHDR, VvDX3, VvTER, VvGT14) was detected in cooled grapes, with variable effects depending on temperature and treatment duration. In both cooled samples, the evolution of alcoholic fermentation followed a regular trend but ended earlier. Higher phenolic content was detected in wines obtained from the 10°C-treated grapes. Higher residual concentration of malic acid at the end of fermentation was detected in wine samples from grapes pre-cooled at 4°C. Sesquiterpenes also showed a general increase in wines from cooled grapes, especially after pre-cooling at 10°C for 48 h. Different sensory profiles characterized the wine samples, with the best scores in terms of general pleasantness obtained by the wine produced from grapes pre-cooled at 4°C for 24 h. These results demonstrate that pre-cooling harvested grapes induces specific effect on the VOC profile and other quality parameters of Vermentino wine, and this appears to be the result of specific metabolic and compositional changes occurring in the berries.
Highlights
The increase of average temperatures characterizing the last decades is affecting the grape-growing and wine sectors [1]
All the samples showed, compared to T0, a general decrease of titratable acidity, with the only exception represented by the grapes kept at 4◦C for 24 h, which showed a TA level similar to that recorded in grapes at harvest
Compared to T0, total polyphenols content (TPC) significantly increased in grapes cooled for 48 h at 10◦C, and a similar trend was observed in grapes cooled at the same temperature for 24 h, while the lowest values were observed in control berries at both sampling time (24 and 48 h)
Summary
The increase of average temperatures characterizing the last decades is affecting the grape-growing and wine sectors [1]. Modesti et al [12] showed that cv Vermentino berries react to a short-term refrigeration (4 or 10◦C) pre-crushing treatment by increasing the concentration of terpenoids, but no information has been provided concerning the resulting wines These data indicate that grape berries react to the imposed stress condition by modifying specific physiological and metabolic processes, resulting in compositional changes, and impacting the quality of the wines. In this context, based on the hypothesis that compositional modifications induced by pre-processing refrigeration could potentially improve grapes and wine quality, our main goal was to evaluate the effect of short-term low temperature conditioning on volatile organic compound (VOC) profile and wine sensory traits. Here, we report both the effects of applying pre-processing cooling (pre-cooling) on specific molecular and metabolic parameters of grapes (cv Vermentino) and the quality traits of the resulting wines
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