Malbec is a wine grape variety that is now mainly produced in Mendoza and considered to be the emblematic cultivar of Argentina. Forty-four phenolic compounds, including hydroxybenzoic and hydroxycinnamic acids and different flavonoids, were identified and quantified in 61 monovarietal Malbec wines from 11 geographical zones of Mendoza province, using a reversed phase high-performance liquid chromatography system coupled to a diode array detector (HPLC-DAD). Among non-flavonoids, gallic, cis-caftaric, trans-coutaric, and caffeic acids presented the higher concentrations in all of the samples, whereas trans-resveratrol glucoside was present at concentrations from 0.6 to 1.3 mg/L. For the flavonoids, (+)-catechin and (-)-epicatechin presented the higher concentrations among flavan-3-ols with a ratio (+)-catechin/(-)-epicatechin from 1.3 to 2.1. An astilbin derivative and quercetin presented the higher concentrations for flavonols, whereas malvidin-3-glucoside and its derivatives were the major anthocyanins. For the first time the phenolic composition of Malbec wines from Mendoza province has been characterized.

The polyphenolic content of Malbec wines was higher compared with the other red varieties. Dihydroflavonols represent a significant finding from the chemotaxonomic point of view, especially for Malbec variety. This is the first report on the individual phenolic composition of red wines from Mendoza (Argentina) and suggests that anthocyanins, flavanols and phenolic acids exert a great influence on cultivar-based differentiation.

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The phenolic composition of Malbec (Vitis vinifera L.) grape skins and seeds during ripening and the effect of cluster thinning (CT) in two consecutive seasons (2008-2009) were evaluated by high-performance liquid chromatography-diode array detection/electrospray ionization-mass spectrometry (HPLC-DAD/ESI-MS). Removal of 50% of clusters was performed at 40 days (T1), 80 days (T2), and 100 days after flowering (T3) in a vineyard located in southern Mendoza (Argentina). Yield components, with the exception of cluster weight, were significantly affected by CT in both seasons, but no statistically significant differences were found among treatments. Cluster thinning and its timing had little or no influence on physical parameters and fruit chemical composition, and the differences with respect to the control were mainly due to the season. At harvest in 2008, T1 encouraged the biosynthesis of individual anthocyanins in skins, generating 44.0, 39.6, and 41.2% more glucosylated, acetylated, and total anthocyanins, respectively, as compared to the control, whereas in seeds, T1 and T2 mainly changed the concentrations of (+)-catechin, epicatechin-3-gallate, procyanidin B4, dimer gallate 1, trimer gallate 2, and tetramer. Conversely in 2009, T1 significantly affected the content of flavanols and flavonols in skins, whereas in seeds, T1 and T2 modified the level of (+)-catechin, procyanidins B4 and B6, and trimer gallate 2. Moreover, in 2008 the grapes had a higher concentration of most phenolic compounds, indicating a greater potential for more complex wines. Finally, dihydroquercetin-3-glucoside was the major compound among all nonanthocyanin phenolics detected in Malbec skins and represented 25.7% (2008) and 39.9% (2009) of the total content of those compounds at harvest. This finding could represent a distinctive feature of this grape variety.

During certain wine fermentation processes, yeasts, and mainly non-Saccharomyces strains, produce and secrete enzymes such as β-glucosidases, proteases, pectinases, xylanases and amylases. The effects of enzyme activity on the aromatic quality of wines during grape juice fermentation, using different co-inoculation strategies of non-Saccharomyces and Saccharomyces cerevisiae yeasts, were assessed in the current study. Three strains with appropriate enological performance and high enzymatic activities, BSc562 (S. cerevisiae), BDv566 (Debaryomyces vanrijiae) and BCs403 (Candida sake), were assayed in pure and mixed Saccharomyces/non-Saccharomyces cultures. β-Glucosidase, pectinase, protease, xylanase and amylase activities were quantified during fermentations. The aromatic profile of pure and mixed cultures was determined at the end of each fermentation. In mixed cultures, non-Saccharomyces species were detected until day 4-5 of the fermentation process, and highest populations were observed in MSD2 (10% S. cerevisiae/90% D. vanrijiae) and MSC1 (1% S. cerevisiae/99% C. sake). According to correlation and multivariate analysis, MSD2 presented the highest concentrations of terpenes and higher alcohols which were associated with pectinase, amylase and xylanase activities. On the other hand, MSC1 high levels of β-glucosidase, proteolytic and xylanolytic activities were correlated to esters and fatty acids. Our study contributes to a better understanding of the effect of enzymatic activities by yeasts on compound transformations that occur during wine fermentation.