ABSTRACT
Aims: To determine the secondary plant metabolites present in Albizia zygia (DC) stembark and investigate its antioxidant, antimicrobial and toxicity activities. Study Design: Methanol (polar) and hexane (non-polar) were used to extract the dried stem bark of A. zygia and biological activities were carried out. Place and Duration of Study: Natural products/Medicinal Chemistry Unit, Department of Chemistry, University of Ibadan, Nigeria, between July, 2012 and February, 2013. Methodology: Chemical methods were used for phytochemical screening. Antioxidant screening was determined by scavenging effect on 2,2-diphenyl-1-picryl hydrazyl (DPPH) and hydroxyl radical generated from hydrogen peroxide methods, agar well diffusion method was used for antimicrobial screening while brine shrimp lethality test was used to determine the toxicity of the extracts. Results: Alkaloid, saponin, glycoside, steroid, resin and reducing sugar were found in both the methanol and hexane extracts while flavonoid and cardio active glycoside were observed only in the hexane extract. The methanol extract had the highest % inhibition at 1.0 mg/ml (93.28%) in the DPPH method and was better than that of ascorbic acid and α- tocopherol. But at 1.0 mg/ml, the n-hexane extract with % inhibition of 78.76% showed better antioxidant activity than butylatedhydroxylanisole (BHA) (40.12%) and α-tocopherol (21.69 %). The antimicrobial activities of the stem extracts of A. zygia against Escherichia coli, Staphylococcus aereus, Bacillus subtilis, Pseudomonas aeruginosa, Klebsiellae pneumonae, Salmonellae typhi, Candida albicans, Rhizopus stolon, Aspergillus niger and Penicillum notatum showed that the methanol extract was more active than n-hexane extract at 50 mg/ml. Brine shrimp lethality test showed that the methanol extract with LC50 of 1.70 μg/ml was more toxic than the non-polar n-hexane extract with LC50 of 174.19 μg/ml. Conclusion: This study underscores the importance of application of A. zygia in ethno medicine and extracts from A. zygia could be used as antioxidant and antimicrobial agents.