Extraction methods for the releasing of bound phenolics from Rubus idaeus L. leaves and seeds

Non-extractable/bound phenolics from plant matrices played an increasingly important role in human health benefits, but conventional solvent extraction missed high amounts of bound phenolics. In this study, Rubus idaeus L. leaves (RDLR) and seeds residues (RDSR) free of extractable phenolics were treated by different methods, respectively. The results revealed that acid, alkaline, and enzymatic hydrolysis can all significant improve the releasing of bound phenolics. Moreover, acid hydrolysis was the most efficient method for releasing the bound phenolics from RDLR and RDSR, followed by enzymatic hydrolysis. The quantitative results showed that most of individual phenolic compounds were significantly enhanced from RDLR and RDSR after acid hydrolysis. Especially for ellagic acid, was increased by 156.1-folds for RDLR and 101.8-folds for RDSR compared with methanol extraction. For RDLR or RDSR, regardless of the hydrolysis methods, higher contents of bound phenolics evidently showed the stronger antioxidant activities and inhibitory potency in α-glucosidase. Importantly, a significantly positive correlation existed in between the investigated bio-activities and bound phenolics/flavonoids released from RDLR or RDSR. These results provided comprehensive approaches for treating the residues of agricultural crops or fruit tree leaves enriched in bound phenolics, thereby to enhance their bio-accessibility.