Characterization of Polyphenolics in Grape Pomace Extracts Using ESI Q-TOF MS/MS

Abstract

Background: Grape pomaces are rich sources of polyphenolics that are reportedly beneficial for health, but their content and quality between red and white pomaces have not been systemically compared. Methods and findings: The current study compared polyphenolics from different grape extracts and further characterized A-type Proanthocyanidins (PAC), which have not been studied previously. The total contents of polyphenolics, flavonoids and PAC and total antioxidant activities of Red Grape Pomace Extract (RGPE) were higher than those in White Grape Pomace Extract (WGPE). Using direct-infusion electrospray ionization tandem mass spectrometry, glucosides of quercetin and peonidin were detected in both RGPE and WGPE, while quercetin, malvidin derivatives and petunidin 3-p-coumaroylgluside only found in RGPE. (epi)catechins, B-type PACs, A-type PAC dimers, and single A-type linked PAC trimers and tetramers were detected in RGPE, WGPE and Grape Seed Extract (GSE). Other singly and doubly charged A-type PACs only detected in GSE. Furthermore, monogalloylated A-type dimers with (epi)cat and (epi)afz were detected in both GSE and WGPE. Conclusion: RGPE contains relatively greater amounts of polyphenolics than WGPE, and more A-type PAC was detected in GSE. The total antioxidant content was higher in RGPE than WGPE.