Evaluation of antioxidant activity of aqueous extract of some selected nutraceutical herbs

The objectives of this study were to examine the antioxidant activities and free radical scavenging effects of extracts of aqueous leaves of Psidium guajava L. (PE), Camellia sinensis (GABA tea; CE), Toona sinensis Roem. (TE) and Rosemarinus officinalis L. (RE). Among the four extracts, PE exhibited the strongest efficiency and showed over 50% scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals at the concentration of 100 μg/mL. The reducing power of four nutraceutical herbs was in the order of PE > RE > CE > TE. The antioxidant activities of nutraceutical herbs were evaluated in a liposomes oxidation system promoted by Fe³⁺/ascorbic acid/H₂O₂. PE still showed the strongest antioxidant activity and exhibited over 95% inhibition at concentration of 50 μg/mL. The antioxidant activity of TE was still lower than that of other herbal plants; however, it also displayed 89% inhibition at concentration of 250 μg/mL. RE exhibited well inhibitory effects on the UVB-induced oxidation of erythrocyte ghosts at lower concentration (100 μg/mL). However, the protection of PE on the UVB-induced oxidation was significantly raised with increasing the concentrations and reached 95.4% inhibitory effects at concentration of 500 μg/mL. These results show that the tested herbal tea, especially PE could be considered as a natural antioxidant source.