Postharvest partial dehydration is a technique used in the production of important dry and sweet wines in Italy. An accurate management of the dehydration environmental parameters allows for the modulation of berry metabolism and the maintenance/improvement of the enochemical quality of grapes. As it is known that water loss induces oxidative processes in berries, our hypothesis was that methyl jasmonate (MeJA) and ozone (O), as postharvest treatments before partial dehydration, might be beneficial for grape berry quality. Grape bunches were postharvest treated with 10 or 100 μM MeJA at 20 °C or with ozone gas at 10 °C, in 70% relative humidity (RH) and air flow, for 12 h; the control bunches were untreated and kept at 20 °C for 12 h. Subsequently, partial dehydration was performed at 10 °C until a 30% weight loss (w.l.) was reached. MeJA hastened grape berry water loss. Polyphenol and flavonoid contents at the end of the partial dehydration were lower in the MeJA-treated berries than in the control and ozone samples. Superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX) activity rates increased in the treated samples. In contrast, lipoxygenase (LOX) and polyphenoloxidase (PPO) had lower activities in the MeJA-treated samples than in the controls. It would seem that MeJA accelerates grape water loss but at the same time activates the antioxidant system. Ozone does not accelerate grape water loss but induces the antioxidant system and increases polyphenol content.
When bushfires occur near grape growing regions, vineyards can be exposed to smoke, and depending on the timing and duration of grapevine smoke exposure, fruit can become tainted. Smoke-derived volatile compounds, including volatile phenols, can impart unpleasant smoky, ashy characters to wines made from smoke-affected grapes, leading to substantial revenue losses where wines are perceivably tainted. This study investigated the potential for post-harvest ozone treatment of smoke-affected grapes to mitigate the intensity of smoke taint in wine. Merlot grapevines were exposed to smoke at ~7 days post-veraison and at harvest grapes were treated with 1 or 3 ppm of gaseous ozone (for 24 or 12 h, respectively), prior to winemaking. The concentrations of smoke taint marker compounds (i.e., free and glycosylated volatile phenols) were measured in grapes and wines to determine to what extent ozonation could mitigate the effects of grapevine exposure to smoke. The 24 h 1 ppm ozone treatment not only gave significantly lower volatile phenol and volatile phenol glycoside concentrations but also diminished the sensory perception of smoke taint in wine. Post-harvest smoke and ozone treatment of grapes suggests that ozone works more effectively when smoke-derived volatile phenols are in their free (aglycone) form, rather than glycosylated forms. Nevertheless, the collective results demonstrate the efficacy of post-harvest ozone treatment as a strategy for mitigation of smoke taint in wine.
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