Antioxidative Activity of Water Extracts of Lagerstroemia speciosa Leaves

In order to develop naturally occurring antioxidants from edible plants, the antioxidative effect of hot water extracts of Lagerstroemia speciosa leaves, known by the Tagalog name of banaba in the Phillipines, was studied. The content of tannin in banaba extract was 36.8% in dry weight. Banaba extract showed strong antioxidative activity in a linoleic acid autoxidation system. Banaba extract was found to have a potent radical scavenging action on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals and superoxide radicals (O(2-) ) generated by a hypoxanthine (HPX)/xanthine oxidase (XOD) system. In vitro lipid peroxidation of rat liver homogenate induced by tert-butyl hydroperoxide (BHP) was inhibited by the addition of banaba extract in a dose-dependent manner. From these results, banaba extract was demonstrated to be useful as an antioxidant or free radical scavenger to protect biological systems against oxidative stress.