Antioxidant activity and quantitative estimation of azadirachtin and nimbin in Azadirachta Indica A. Juss grown in foothills of Nepal

The leaf and bark fraction extracts of Azadirachta indica A. Juss. (neem) grown in the foothills (subtropical region) of Nepal were evaluated for their antioxidant activity, total phenolic (TP) and total flavonid (TF) contents. HPLC method was employed to quantify the amount of azadirachtin and nimbin present in the seed, leaf and the bark extracts of neem. The result showed that the highest azadirachtin content was found in the methanolic extract of the seed (3300 μg/g dw). Similarly, the hexane fraction of bark showed the highest nimbin content (271 μg/g dw) followed by the methanolic extract (260 μg/g dw). Antioxidant activity was determined by measuring 1,1-diphenyl-2-picrylhydrazyl free radical scavenging activity, hydroxyl radical scavenging activity, DNA protection assay, metal chelating and the inhibition of peroxidation using linoleic acid system and their results were found at different magnitudes of potency. The results of TP content expressed in tannic acid equivalents ranged from 66.63 to 629.04 μg/mg in the bark extracts and 23.85 to 237.00 μg/mg in the leaf extracts. Likewise, the content of TF expressed in quercetine equivalents ranged from 12.87 to 17.07 μg/mg in the bark and 13.72 to 93.17 μg/mg in the leaf extracts.