α-Glucosidase inhibition and antioxidant activity of an oenological commercial tannin. Extraction, fractionation and analysis by HPLC/ESI-MS/MS and 1H NMR.

Two batches of the oenological tannin Tan’Activ R, (toasted oak wood – Quercus robur), were extractedwith ethanol. A fractionation on XAD-16 afforded four fractions for each extract. Extracts and fractionswere evaluated for antioxidant activity (DPPH), polyphenol content (GAE) and yeast a-glucosidase inhibitoryactivity. Comparable results were obtained for both columns, fractions X1B and X2B showing thehighest antioxidant activity. Fractions X1C and X2C notably inhibited a-glucosidase, with IC50 = 9.89 and8.05 microg/mL, respectively. Fractions were subjected to HPLC/ESI-MS/MS and 1H NMR analysis. The mainphenolic constituents of both X1B and X2B were a monogalloylglucose isomer (1), a HHDP-glucoseisomer (2), castalin (3) gallic acid (4), vescalagin (5), and grandinin (or its isomer roburin E, 6). X1Cand X2C showed a complex composition, including non-phenolic constituents. Fractionation of X2C gavea subfraction, with enhanced a-glucosidase inhibitory activity (IC50 = 6.15 microg/mL), with castalagin (7) asthe main constituent.