Characterizing the antioxidant activity of amla (Phyllanthus emblica) extract

Amla is well-known for its rich vitamin C (ascorbic acid) and polyphenol contents. To assess its antioxidant activity, we examined aqueous amla extract for its ability to inhibit gamma -radiation-induced lipid peroxidation (LPO) in rat liver microsomes and superoxide dismutase (SOD) damage in rat liver mitochondria. For the LPO experiment, amla extract was added as its aqueous solution; and irradiation was carried out at different time intervals. The extent of LPO was measured in terms of thiobarbituric acid reactive substances. It was observed that the amla extract acts as a very good antioxidant against 7-radiation-induced LPO. Similarly, it was found to inhibit the damage to antioxidant enzyme SOD. The antioxidant activity of the amla extract was found to be both dose- and concentration-dependent. The amount of ascorbic acid in amla was standardized by HPLC and titrimetric methods and was found to be 3.25 to 4.5% w/w. However in microsomes containing this composition of pure ascorbic acid alone, no inhibition in LPO was observed. Cyclic voltammetry of the amla extract was carried out to estimate the ascorbic acid equivalents, which was found to be 9.4% w/w of amla. This value was found to be in agreement when compared with the reactivity of both amla and ascorbic acid towards ABTS(.-) radical, a stable free-radical. Based on these results it is concluded that amla is a more potent antioxidant than vitamin C.