In vitro antioxidant, total phenolic, membrane stabilizing and antimicrobial activity of Allamanda cathartica L.: A medicinal plant of Bangladesh

The methanol extract of the leaf of Allamanda cathartica L. as well as its hexane, carbon tetrachloride, chloroform and aqueous soluble partitionates were subjected to screening for antioxidant, membrane stabilizing and antimicrobial activities. The antioxidant potential was evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and Folin-Ciocalteau reagents using butylated hydroxytolune (BHT) and ascorbic acid as standards. The carbon tetrachloride soluble fraction revealed the highest free radical scavenging activity (IC50 = 47.5±0.11 μg/ml) which could be correlated to its total phenolic content of 59.31±0.47 mg of gallic acid equivalent (GAE)/g of extractives. In hypotonic solution and heat induced conditions, the aqueous soluble fraction inhibited haemolysis of human erythrocyte by 69.49±0.49 and 40.0±0.75%, respectively. Here, acetyl salicylic acid (0.1 mg/ml) was used as reference showing 72.79 and 42.12% of haemolysis of red blood cells (RBCs) in hypotonic solution and heat induced conditions, respectively. The carbon tetrachloride soluble fraction of A. cathartica demonstrated activity against microbial growth with zone of inhibition ranging from 5.0 to 8.5 mm. This fraction demonstrated 8.5 mm zone of inhibition against Bacillus megaterium. Key words: Allamanda cathartica, total phenolic content, 1,1-diphenyl-2-picrylhydrazyl (DPPH), free radical scavenging activity, membrane stabilizing activity, zone of inhibition.