Adsorção de antocianinas por leveduras e sua influência na coloração de vinhos

Abstract

The intensity and color tone of red wines are among the main quality attributes of the final product. The color of red wines is dependent on the concentration of pigments, mainly anthocyanins, which are extracted from the skins of the grapes during the fermentation process. The yeasts can reduce the color intensity and modify the wine hue by the direct adsorption of pigments, however, the way how this process occurs still needs to be elucidated. In addition, the currently existing methods for the evaluation of the adsorption capacity of pigments by yeasts are limited and, in general, they are time-consuming and inadequate for a large number of strains. Therefore, the objective of this study was to develop a method to assess the adsorption of pigments by yeasts in wines and to elucidate the factors that determine the differential adsorption of pigments by different yeast strains during wine fermentation. Initially, 22 commercial yeast strains of Saccharomyces cerevisiae, three commercial yeast strains of S. cerevisiae, and one commercial yeast strain of Torulaspora delbrueckii were used in microfermentation of musts of Merlot, Cabernet Sauvignon, and Ives grape varieties. The fermentations (800 µL) were conducted in plates with 96 cell culture wells (2.2 mL capacity), kept at 25°C, and vortex agitated once a day. At the end of the fermentation (14 days), the cells were removed by centrifugation and, the wine was transferred to a 96-well plate and the intensity and tonality evaluated in a microplate reader (420 and 520 nm). The cells were transferred to a 96-well cell culture plate, then the plate was digitized in a scanner and analyzed in a graphic program to determine the adsorption of pigments. From these results, three groups of yeasts were selected to assess the capacity of individual cells to adsorb pigments by flow cytometry. The integrity of the cell membrane of the yeasts was validated by the exclusion of Trypan Blue. The results show a significant negative correlation between adsorption of pigments by yeasts and wine color intensity. The adsorption of pigments occurs at the end of the fermentation, indicating alterations in the cell wall and/or modifications of the anthocyanins during the process. Significant differences were observed in the adsorption of anthocyanins and in the wine color intensity between yeast strains, regardless of the grape variety, and the yeasts could be grouped into low, medium, and high adsorption. The proposed method showed high reproducibility and allows the evaluation of a large number of yeast lines. It was observed that the strains with high anthocyanin adsorption capacity showed sufficient fluorescence to be differentiated by flow cytometry. The fluorescence of the cells was negatively correlated with the viability of the same. Regardless of the potential of a yeast line to adsorb anthocyanins, living cells show low adsorption capacity, whereas permeabilized cells show high anthocyanin adsorption capacity. The work contributed with alternatives for the determination of the adsorption capacity of pigments by yeasts, in addition the data showed that the integrity of the wall/membrane is the main variable involved in the adsorption capacity of anthocyanins by yeasts. [resumo fornecido pelo autor]