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This study was aimed at evaluating antibacterial and antioxidant activity of tannins extracted by several solvents from agricultural by-products, including green tea waste and acorn, chestnut, and persimmon hulls. Tannin content was the highest in acetone extracts from all types of hulls, but not green tea waste (p<0.05). Tannin extracts from green tea waste had higher antibacterial activity than those from acorn, chestnut, and persimmon hulls extracted with distilled water, ethanol, or acetone. With ethanol extraction, 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity of green tea tannin extracts was significantly higher than that of tannins extracted from acorn, chestnut, and persimmon hulls (p<0.05). In particular, tannins extracted from green tea waste had a greater IC50 value for DPPH scavenging activity than did vitamin C. Antioxidant activity was also significantly higher in ethanol extracts from green tea waste than in distilled water and acetone extracts (p<0.05). Therefore, tannins extracted from green tea waste could be a natural source for substitutes to present antioxidants as well as antibiotics. Key words: Acorn, antibacterial activity, antioxidant activity, chestnut, green tea, persimmon.
Si Heung Sung (Wed,) studied this question.