Postharvest treatment with chitosan affects the antioxidant metabolism and quality of wine grape during partial dehydration

The effectiveness of postharvest chitosan treatments on qualitative traits and antioxidant biochemical system during postharvest partial dehydration of "Sagrantino" grape has been studied, compared with ozone postharvest treatment. One % and 2% chitosan coatings delayed water loss but no difference in berry color or peel resistance during partial dehydration up to 30% mass loss (m. l.), was found among samples. The reducing sugar content rose straightly from 275 g L-1 (harvest), up to 445, 428, 411, and 390 g L-1, in 2% chitosan, 1% chitosan, water, and ozone, respectively. Malic acid, and consequently total acidity, increased progressively in all samples with higher values in ozone-and in chitosan-treated berries. In all samples, total polyphenol content rose already at 10% m. l., and 1% chitosan sample had the highest value. Postharvest treatments enhanced the activity of antioxidant enzymes, superoxide dismutase (SOD) and ascorbate peroxidase (APX), during partial dehydration process, whereas inhibited polyphenoloxidase (PPO) and lipoxygenase (LOX) activity, preventing polyphenol loss and avoiding membrane oxidation, as shown by lower malondialdehyde (MDA) accumulation.