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

The gallotannins of Gallo chinensis (Chinese gallotannins, CGTs) were identified using LC-MS, and their numbers of isomers in different extracts of Gallo 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 mu g/mL) in the beta-carotene-linoleic acid system assay. The antibacterial activity of CGTs against Salmonella typhimurium (Grain 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. (C) 2009 Elsevier Ltd. All rights reserved.