An investigation on polyphenol composition and content in skin of grape (Vitis vinifera L. cv. Hutai No.8) fruit during ripening by UHPLC-MS2 technology combined with multivariate statistical analysis

Polyphenols, a class of biologically active substances related to grapes quality, differ with maturity. This study aimed to evaluate polyphenol composition, content and antioxidant capacity of skin polyphenol extracts in Hutai No. 8 grape (Vitis vinifera L.) at five key ripening stages: full-green (FG), red-appeared (RA), half-red (HR), full-red (FR) and purple-black (PB), and to identify the polyphenolic compounds that had a potential to be markers for distinguishing the ripening stages. Grape skin extract at each ripening stage was studied for their total phenolic content (TPC), total flavonoid content (TFC) and the antioxidant capacity. Results showed a significant difference in accumulation of polyphenols at five stages. A trend towards an increase in TPC, TFC, and antioxidant capacity was observed during ripening. Then, this study profiled the polyphenolic compounds of grape skin at each ripening stage by UHPLC-ESI-qTOF-MS2 and UHPLC-QQQ-MS2. Results revealed that a total of 18 polyphenolic compounds were identified. Polyphenols were quantified according to phenolic class. And catechin was the major flavanol in skin, which was observed the highest content at the HR stage. Furthermore, quercetin-3-O-glucoside, 1-O-vanilloyl-beta-D-glucose and resveratrol-3-O-glucoside were respectively considered as the representative phenolic acid and stilbene, all of which were detected the highest at the PB stage. Moreover, polyphenolic compounds that had a potential to be markers for distinguishing the ripening stages of Hutai No.8 grape were identified through orthogonal partial least squares discriminant analysis (OPLS DA). Results indicated that catechin, epicatechin, quercetin-3-O-glucoside, myricetin, isorhamnetin-3-O-hexose and resveratrol-3-O-glucoside were the vital markers. The study provides a reference for differentiating grapes at different ripening stages based on polyphenols.

Automated summary

This study evaluated the polyphenol composition, content, and antioxidant capacity of grape skin extracts at five key ripening stages, identifying potential markers for distinguishing ripening stages. Results showed significant differences in polyphenol accumulation at different stages, with an increasing trend in total phenolic content, total flavonoid content, and antioxidant capacity during ripening. Analysis of polyphenolic compounds identified catechin, quercetin-3-O-glucoside, and resveratrol-3-O-glucoside as potential markers for distinguishing ripening stages.