Grape postharvest ozone treatments: impact on berry skin stilbenes content after short and continuous exposure.

The use of postharvest ozone treatments on grapes, already proposed in literature for the postharvest control of microbiota, was also related by some authors to a combination of oxidation and elicitor effects on several grape components. Treatment time and ozone concentration are considered important factors for determining the treatment effectiveness. Some of the molecules involved in these effects are related to the antioxidant fraction, considered of high importance and well-studied for their health benefits. To evaluate the possible ozone treatment effects during postharvest storage, 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 gaseous ozone concentrations (30 and 60 μL/L) were compared to a control sample by means of berry skin resveratrol and stilbenes contents. 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% berry weight loss. At 24 or 48 hours ozone-enriched atmosphere exposure, Moscato grapes showed no significant changes in resveratrol content, although the highest contents after treatment and after 7 days from treatment were found using a 48-hours, 60-μL/L atmosphere ozone treatment. During grape dehydration, resveratrol contents decreased in both control and ozone-treated samples with respect to fresh grapes, with a steep decrease until 5% weight loss, followed by a slight increase between 5 and 15%. At the end of the dehydration process, there were no significant differences between control and ozone-treated samples.