The effect of cluster thinning on wine composition, total phenolics, total anthocyanins, antioxidants, and resveratrol content of the winegrape cultivar Chambourcin (Vitis spp.) was studied over three years. Titratable acidity and pH of samples were determined using standard methodology; total phenolic, anthocyanin concentration, and antioxidant capacities of wines were measured spectrophotometrically after incubation with specific reagents. Levels of cis- and trans-resveratrol and their glycosides (piceids) in wine samples were analyzed by direct injection into HPLC coupled with photodiode array detection. Cluster thinning did not affect basic wine composition except pH. Cluster thinning, however, increased linearly the polyphenolic composition of wines as indicated by increases in total anthocyanins, total phenolics, and antioxidant capacity. Cluster thinning also increased linearly the total resveratrol level including free resveratrol (cis- and trans-) and its glycoside derivatives (cis- and trans-piceids). Positive correlations were found between total phenolics, total anthocyanins, resveratrol, and antioxidant capacity. It was concluded that cluster thinning of Chambourcin produced wines with increased anthocyanins, total phenolics, and antioxidant capacity and thus wines with increased potential health benefits.
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