Phytochemicals and Antibacterial Activity of Leaf and Twig of Three Fabaceae Species

The Fabaceae family is known for producing a diverse range of secondary metabolites having biological activity, including analgesic, anti-inflammatory, anticancer, antidiabetic, antirheumatic, antibacterial, and cytotoxic properties. Three Fabaceae species, Pterocarpus indicus, Adenanthera pavonina, and Falcataria falcata, possess pharmacological potential that has not been thoroughly investigated. The goals of this study were (1) to determine the antibacterial activity against Bacillus subtilis and Escherichia coli of leaves and twigs extract of these three Fabaceae species and (2) to identify the putative secondary metabolites in the leaves and twigs of the species exhibiting the lowest minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against B. subtilis and E. coli. The dried leaves and twigs of P. indicus, A. pavonina, and F. falcata were extracted using ultrasonic-assisted extraction, followed by an antibacterial bioassay utilizing broth dilution procedures. Qualitative and semiquantitative phytochemical screening was then carried out. Chemical substances were detected using liquid chromatography-mass spectrometry (LC-MS) analysis. F. falcata leaves methanol extract had MIC 1.30 mg/mL and MBC 5.00 mg/mL against B. subtilis and had trice higher antibacterial activity than P. indicus and A. pavonina. However, F. falcata leaves ethyl acetate extract had MIC 0.30 mg/mL and MBC 1.0 mg/mL against E. coil, twice higher than P. indicus and A. pavonina extract. This also positively correlated with the flavonoid contents obtained; F. falcata leaves ethyl acetate extract had higher, that is, 43.93 ± 3.56 mg QE/g extract. However, the highest total phenolic content was found in the methanol leaf extract of P. indicus, although the methanol leaf extract of F. falcata was still relatively large, namely, 172.79 ± 1.51 mg gallic acid equivalent (GAE)/g extract. LC-MS analysis revealed that F. falcata extract included phenolics, flavonoids, terpenoids, and carboxylic acids. Almost all extracts contained the active component kaempferol.