Identification and structure–activity relationship of gallotannins separated from Galla chinensis

The gallotannins of Galla chinensis (Chinese gallotannins, CGTs) were identified using LC–MS, and their numbers of isomers in different extracts of Galla chinensis were determined. The antioxidant activities of CGTs with different degree of galloylation were evaluated in four antioxidant systems. Their antioxidant activities increased with increasing number of galloyl groups in all four antioxidant tests. CGTs had a dose–response relationship at the low concentrations (15–60 μg/mL) in the β-carotene–linoleic acid system assay. The antibacterial activity of CGTs against Salmonella typhimurium (Gram negative) and Bacillus cereus (Gram positive) was assessed using the paper disc diffusion method. Hexa-hepta-galloylglucopyranoses (6–7GGs) showed the best antibacterial activities. In general, 6–7GGs possessed antioxidant and antibacterial activities greater than BHT, Trolox, or Ethylparaben. Moreover, an insight on the structure–activity relationship of CGTs is discussed.