Characterization of phenolic profile in dried grape skin of Vitis vinifera L. cv. Pinot Blanc with UHPLC-MS/MS and its development during ripening

Comprehensive phenolic composition of dried grape skin from cv. Pinot Blanc and its development during ripening is reported, with particular emphasis on flavonol glycosides profile. Extraction procedure and reversed-phase ultra-high-performance liquid chromatography-triple quadrupole mass spectrometry (UHPLC-QqQ-MS/MS) method were optimized and validated for the determination of 39 phenolic compounds belonging to different groups (flavonols, dihydroflavonols, benzoic and hydroxycinnamic acids, flavan-3-ols). Beside selected reaction monitoring (SRM) for analytes available as standards, flavonols and dihydroflavonols profile was furtherly explored performing precursor ion scan (PIS) with neutral loss (NL) for unavailable compounds. Quercetin-3-O-rutinoside occurred as major flavonol component, and rutinosides for kaempferol- and isorhamnetin- structures were also quantitable. Presence of different myricetin derivatives was unveiled, with myricetin-3-O-glucoside being quantifiable at all ripening time points. Besides high levels of astilbin, dihydroquercetins profile resulted highly complex. Moreover, ratio between caftaric and coutaric acid and between isomers of coutaric acid at harvest was uncommon if compared to other white cultivars.