Multifunctional Antioxidant Activities of Alkyl Gallates

A series (C 1 to C 16 ) of alkyl gallates was tested for their antioxidant activity for food protection and human health. One molecule of alkyl gallate, regardless of alkyl chain length, scavenges six molecules of 1,1-diphenyl-2- picrylhydrazyl (DPPH). Alkyl gallates inhibited the linoleic acid peroxidation catalyzed by soybean lipoxygenase-1 (EC 1.13.11.12, Type 1) without being oxidized. The progress curves for enzyme reactions were recorded by both spectropho- tometric and polarographic methods and the inhibitory activity was a parabolic function of their lipophilicity (log P) and maximized with alkyl chain length between C 12 and C 16 . Tetradecanyl (C 14 ) gallate exhibited the most potent inhibition with an IC 50 of 0.06 µM. The inhibition kinetics of dodecyl gallate (C 12 ) revealed competitive and slow-binding inhibi- tion. Alkyl gallates chelate transition metal ions and this chelation ability should be of considerable advantage as antioxi- dants. Additionally, gallic acid was found to inhibit superoxide anion generated by xanthine oxidase (EC 1.1.3.22) but did not inhibit enzymatically catalyzed uric acid formation.