Characterization of phenolic compounds present in Neem leaf extracts using HPLC and determination of their antioxidant activity

Indian Neem (Azadirachta indica L.) leaf was extracted by three different extraction methods (Decoction, Percolation and Maceration) using two different solvents; methanol 80% (v/v) and water. Determination of total phenolic content by Folin-Ciocalteu method revealed that methanol 80% (v/v) for 7 days (maceration method) cause the highest quantity of extracted phenolic compounds. Meanwhile, determination of radical scavenging activity of three different extracts by DPPH method indicated that methanol 80% (v/v) for 24 h (percolation method) cause the highest RSA and was considered as the most effective extract. Furthermore, qualitative and quantitative characterization of phenolic compounds of percolation extract as the effective extract using HPLC revealed that Nimbolide (2896.05 mg/100 g extract) is the main limonoid triterpen followed by phenolic acids and 2′, 3′-dehydrosalannol which are 635.38 and 531/94 mg/100g extract, respectively. Determination of antioxidative effects of percolation extract in refined soybean oil (without antioxidant) using accelerated oven test (13 days, 60℃) declared that soybean oil containing 2000 ppm of the percolation extract was more stable than other concentrations until 4th day in terms of hydroperoxide when the aforementioned concentration was able to make the oil more stable until 13th day in terms of aldehydes and ketones.