Comparative in vitro antioxidant and antibacterial activities of leaf extract fractions of Crimson bottlebrush, Callistemon citrinus (Curtis.) Skeels

ObjectivesThe present study aimed to analyze a comparative in vitro free radical scavenging and antibacterial potentials of leaf aqueous and the successive extract fractions of Callistemon citrinus. MethodsFor in vitro antioxidant activity assessments, 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity, Fe3+ ion reducing antioxidant power (FRAP) assay, and total antioxidant capacity of the extracts were tested. Antibacterial potentials were tested through Agar well diffusion method using both gram-positive and gram-negative bacterial strains. ResultsData indicate the polar successive aqueous fraction (AQF) possesses the highest free radicals scavenging capacity, with lowest EC50 (the required extract concentration to scavenge half of the free radicals) for DPPH and FRAP assays, and contains the highest total phenolics (308.2{+/-}5.9 {micro}g tannic acid equivalent/mg dry extract, DE), flavonoids (516.7{+/-}3.5 {micro}g quercetin equivalent/mg DE), total antioxidant capacity (441.48{+/-}12.8 {micro}g ascorbic acid equivalent/mg DE). Phenolics and flavonoids contents were positively correlated with the in vitro antioxidant activities. The antibacterial study indicates the petroleum ether and chloroform are suitable solvents for extracting antibacterial phytochemicals from C. citrinus leaves that are effective against both gram-positive and negative bacterial strains. ConclusionThe most polar fraction i.e. the successive aqueous extract fraction of C. citrinus leaves exhibited the highest antioxidant activities while the most non-polar petroleum ether extract fraction showed the highest antibacterial potentials thus these extract fractions might have therapeutic importance.