Antioxidant Guided Fractionation of Blackberry Polyphenols Show Synergistic Role of Catechins and Ellagitannins

Abstract

In the present study, blackberry extract was prepared using a previously optimized solid–liquid extraction method in 70% aqueous acetone aimed at the recovery of its principal phenolics. Subsequently, 0.5 g of freeze-dried extract was subjected to flash chromatography fractionation, which was conducted on a C18 column using a binary solvent system of water and methanol at 10 mL/min. The total phenolic content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and ferric reducing antioxidant power (FRAP) activities of the obtained 42 flash fractions were determined, and a strong positive correlation (r ≥ 0.986) was exhibited among them. Furthermore, the graph of the antioxidant indices of the flash fractions resembled the flash chromatogram, suggesting a good correlation among the compounds within the chromatographic peaks and the antioxidant indices. LC-MS/MS identified as many 28 phenolics, including cinnamtannin A2 reported for the first time in blackberries. This study further established the role of dominant anthocyanins (cyanidin-3-O-glucoside and cyanidin-3-O-rutinoside), but uniquely those of ellagitannins and catechins on the antioxidant capacity of blackberries.