Impact of Solvent Selection on Phytochemical Content, Recovery of Tannin and Antioxidant Activity of Quercus Infectoria Galls

Introduction: Quercus infectoria (QI) is medicinal plant well known to exhibit enormous therapeutic values. The main medicinal part of QI plant exists in its edible nutritious gall. This study aimed to determine the effects of extraction solvents on the overall phytochemical content, recovery of tannin and antioxidant activity of the QI galls. Methods: Two solvents of different polarity namely water and methanol, were used to extract bioactive compounds from the QI galls using soxhlet extraction technique. Phytochemical, TLC and HPLC assays were performed to detect and quantify the extracted compounds. DPPH assay was conducted to evaluate the antioxidant potential of the extracted compounds. Results: After 6 hours of extraction at respective solvent boiling points, methanol solvent successfully generated 1.8-fold higher crude yield (34.0%) compared to water solvent (18.9%). Phytochemical analysis revealed that both solvent extracts contained different secondary metabolites. The methanol extract was found richer in flavonoid, while the aqueous extract was found richer in phenol, tannin, gallotannin, triterpene and cardiac glycosides. Interestingly, we found that the major type of tannin presence in QI galls was gallotannin (hydrolysable tannin) instead of phlobatannin (non-hydrolysable tannin). The quantification results demonstrated that QI aqueous extract contained significantly higher gallotannin (75.0 μg/mL) compared to QI methanol extract (46.8 μg/mL). Furthermore, the aqueous extract also exhibited significant higher antioxidant activity compared to the methanol extract at concentration of 2 μg/mL. Conclusions: This study strongly support the utilization of water solvent for optimum gallotannin extraction from QI galls.