Abstract: To explore an efficient and feasible extraction procedure for the removal of tannins in Quercus acutissima acorns for comprehensive exploitation of Quercus acutissima acorns, the factors affecting the removal rate of tannins from Quercus acutissima acorns collected from Qiaoshan Mountains by ultrasonic-assisted extraction using ethanol as extraction solvent were firstly investigated by one-factor-at-a-time method and then the significant ones were selected and further optimized by response surface methodology. Besides, the antioxidant activity of the tannins extracted was determined by testing 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and hydroxyl radical (·OH) scavenging capacity. Our results demonstrated that liquid-to-solid ratio, ethanol concentration, extraction temperature and ultrasonic power were found to be the factors with a significant effect on the removal efficiency of tannins. The proposed model showed good fitness. An ethanol concentration of 53%, a liquid-to-solid ratio of 42:1 (mL/g), an extraction temperature of 65 ℃ and an ultrasonic power of 240 W were found to be optimal for maximum removal rate of tannins (37.27%). The antioxidant activity of the tannins extracted was positively linearly correlated with their concentration, and the scavenging percentages for DPPH and hydroxyl radical radicals were respectively 75.56% and 62.74% at a tannin concentration of 80 mg/L. Hence, the tannins can be used a new antioxidant.

Key words: Quercus acutissima acorn, tannin extraction, Box-Behnken experimental design, response surface methodology; antioxidant activity