From pulp to pomace: Distribution and bioactivity of free and bound phenolics in Rosa roxburghii

The functional properties of Rosa roxburghii phenolics are governed by their distribution among free (FP), ester-bound (EP), glycoside-bound (GP), and insoluble-bound forms (IBP). In this study, these four fractions were systematically profiled in pulp (RTP), seed (RTS), seedless pomace (SRTP), and seeded pomace (RTPS) using total phenolic content (TPC) and total flavonoid content (TFC), UHPLC-QTOF-MS with targeted MS/MS confirmation, antioxidant assays (DPPH, ABTS, FRAP), α-glucosidase inhibition assays, and chemometric modelling. Free phenolics were found to predominate across all tissue types, exhibiting the highest TPC, TFC, and antioxidant capacities, with pulp and pomace outperforming seeds. Strong in vitro α-glucosidase inhibition was observed in RTP-EP and RTPS-FP, both of which demonstrated lower IC₅₀ values than acarbose and exhibited mixed-type inhibition kinetics. Metabolomic analysis annotated 59 phenolic compounds, with catechin, epicatechin, and isoquercitrin enriched in FP fractions. Principal component analysis (PCA) and Pearson correlation analysis revealed strong associations between antioxidant activity and these specific flavonoids. These findings establish pomace as a rich source of bioactive phenolics and provide a mechanistic and compositional basis for the targeted recovery and application of R. roxburghii phenolics in functional food and nutraceutical formulations.