Antioxidant properties of herbal extracts selected from screening for potent scavenging activity against superoxide anions

BACKGROUND: In a previous study with the electron spin resonance (ESR) spin-trapping method on large-scale screening with ethanol extracts of approximately 1000 kinds of herbs, four herbal extracts with prominently potent ability to scavenge superoxide anions were chosen, namely the extracts from Punica granatum (peel), Syzygium aromaticum (bud), Mangifera indica (kernel) and Phyllanthus emblica (fruit)). In the present study, these extracts were further examined to determine if they also scavenge hydroxyl radicals, by applying the ESR spin-trapping method, and if they have heat resistance as a desirable characteristic feature.RESULTS: Experiments with the Fenton reaction and UV irradiation of hydrogen peroxide, both of which generate hydroxyl radicals, showed that all four extracts had potent ability to directly scavenge hydroxyl radicals. Each extract exerted more potent hydroxyl radical-scavenging activity than mannitol and salicylic acid. Furthermore, the scavenging activities against superoxide anions and hydroxyl radicals of the extracts of P. granatum (peel), M. indica (kernel) and P. emblica (fruit) proved to be heat-resistant.CONCLUSION: The four herbal extracts chosen from extensive screening possess desirable antioxidant properties. In particular, three of them are expected to be suitable for food processing in which thermal devices are used, because of their heat resistance.