Impact of postharvest ozone treatments on the berry skin resveratrol content: short and continuous exposure.

Gaseous ozone treatments on wine grapes were already proposed in literature for the postharvest control of microbiota [1], assuring the safety and quality management of wine production. Some authors pointed out the possible effect of ozone treatments with regards to elicitor actions towards stilbenes contents [2], but only on table grapes. To evaluate the effect at high ozone concentrations, a study was conducted on Vitis vinifera L. cv. Moscato bianco, a white grape cultivar used for the production of sweet and passito wines. Two different experiments were carried out: in the first study short exposures (24 and 48 hours) at two different gaseous ozone concentrations (30 and 60 μL/L) was compared to a control sample by means of resveratrol, piceid, piceatannol, and viniferin berry skin contents, analyzed after treatment and after 7 days from the treatment. In the second study, a long exposure to gaseous ozone (30 μL/L) was carried out during grape dehydration (18°C, 80% relative humidity), and then compared with a control sample at 5, 10, 15, 20, and 30 % weight loss points. A 24 or 48-hours ozone exposure of Moscato grapes shown non-significant changes in resveratrol content, although the higher contents analyzed after treatment and after 7 days from treatment were found in the 48-hours, 60 μL/L treatment. A longer exposure during grape dehydration evidenced that resveratrol contents decreased in both control and treated samples during dehydration with respect to fresh grapes, with a steep decrease until 10 % of weight loss, followed by a slight increase at 15 and 20 % points. At the end of the dehydration process there were almost no differences between control and ozone-treated samples. The dehydration phase comprised between 10 and 15 % weight loss confirmed as critical for the postharvest dehydration process, even for control and ozone treated samples.