Elucidations on the structures of some putative flavonoids identified in postharvest withered grapes (Vitis vinifera L.) by quadrupole time-of-flight mass spectrometry.

Grape dehydration is an oenological process used for production of high-quality reinforced and sweet wines. High-resolution mass spectrometry (ultrahigh-performance liquid chromatography/quadrupole time-of-flight [UHPLC/QTOF]) was used to deepen the characterization of some flavonoids previously proposed in Corvina and Raboso Piave withered grapes. By performing a targeted data analysis workflow and orthogonal identification approaches (tandem mass spectrometry [MS/MS]), in silico fragmentation, and calculation of putative retention time), elucidation on the structures of six compounds previously proposed was achieved (taxifolin-pentoside, two tetrahydroxyflavanone-hexoside derivatives, a tetrahydroxy-dimethoxyflavanone-hexoside derivative, a pentahydroxyflavone, and peonidin-O-pentoside); and the structures of four putative new grape flavonoids were characterized (dihydromyricetin-O-hexoside, taxifolin-di-O-hexoside, isorhamnetin, and a pinoquercetin isomer). Findings enlarge the panorama of flavonoids in grape and of their possible biosynthetic pathways.