Characterisation of polymeric skin and seed proanthocyanidins during ripening in six Vitis vinifera L. cv

The polymeric proanthocyanidin (PAs) composition of skins and seeds from Vitis vinifera L. cv during ripening was evaluated. Six grape varieties (Cabernet Sauvignon, Malvasia bianca, Moscato bianco, Nascetta, Nebbiolo and Pinot bianco) cultivated in Piedmont (vintage 2008) were collected at five different ripening stages (from 6 to 20 °Brix). Polymeric proanthocyanidins were determined both by vanillin assay and by phloroglucinolysis; these analytical methods were compared showing a significant correlation (r = 0.8321, p < 0.0001 and r = 0.7406, p < 0.0001 for grape skins and seeds, respectively). Acid-catalysed cleavage of the polymer, combined with HPLC separation, enabled quantification of individual polymer subunits, estimation of mean degree of polymerisation (mDP), and the evolution of the extractable polymeric fraction isolated during ripening. Antiradical activity was evaluated as inhibition percentage of DPPH radical. A significant positive correlation between total PAs content and antiradical activity was observed (r = 0.6410, p < 0.0001); on the contrary, the mDP appeared to be negatively correlated to the antiradical activity (r = -0.6238, p < 0.0001).