The Open Bioactive Compounds Journal

2010, 3 : 1-11
Published online 2010 January 27. DOI: 10.2174/1874847301003010001
Publisher ID: TOBCJ-3-1

RESEARCH ARTICLE
 Multifunctional Antioxidant Activities of Alkyl Gallates

Isao Kubo, * , Noriyoshi Masuoka , Tae Joung Ha , Kuniyoshi Shimizu and Ken-ichi Nihei
Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720-3114, USA

* Address correspondence to this author at the Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720-3114, USA; Tel: +1-510-643-6303; Fax: +1-510-643-0215; E-mail: ikubo@berkeley.edu

ABSTRACT

A series (C1 to C16) 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 spectrophotometric and polarographic methods and the inhibitory activity was a parabolic function of their lipophilicity (log P) and maximized with alkyl chain length between C12 and C16. Tetradecanyl (C14) gallate exhibited the most potent inhibition with an IC50 of 0.06 µM. The inhibition kinetics of dodecyl gallate (C12) revealed competitive and slow-binding inhibition. Alkyl gallates chelate transition metal ions and this chelation ability should be of considerable advantage as antioxidants. 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.

Key Words:

Antioxidant activity, alkyl gallates, multifunction, scavenger, soybean lipoxygenase-1, xanthine oxidase, antimicrobial activity.