Daniela Borsa

Focusing on bioactive compounds in grapes: stilbenes in Uvalino cv.

Phenolic compounds belonging to the group of stilbenes have recently received a particular attention as bioactive compounds because of their role in plant physiology and for their antioxidant properties. Monomer stilbenes in grapes are mainly present as glycosides. The aim of this work was the identification and quantification of monomer stilbenes (as both free and glycosilated form) in Uvalino grapes, a grapevine variety known for its significant content in stilbenes. Their content in grapes was determined during ripening and overripening stages, in comparison with other phenolic compounds. Piceid (cis and trans form), piceatannol (cis and trans form), cis resveratrol and trans-pterostilbene were identified and quantified in grape skin. Piceid was the most abundant stilbene as both cis and trans forms. As for anthocyanins, the synthesis and the stilbenes accumulation started during veraison, and then, the content of these molecules remained constant with the exception of piceid, whose content slightly increased until harvest. Therefore, stilbenes accumulation seems not to be affected by anthocyanins synthesis. On the contrary, proanthocyanidins, flavonols and hydroxycinnamyl tartrates decreased during ripening. When withering was applied to grapes as a post-harvest treatment, the content of anthocyanins, proanthocyanidins and of the most abundant stilbenes increased, while flavonols and hydroxycinnamyl tartrates decreased. The results suggest that degradation processes during withering are probably weaker or absent in the case of stilbenes, anthocyanins and proanthocyanidins.