Phytochemical screening, total polyphenol, flavonoid content, in vitro antioxidant and antibacterial activities of Sri Lankan varieties of Murraya koenigii and Micromelum minutum leaves

The use of plant materials in traditional medicine as a significant ingredient in synthesizing drugs in the form of decoctions had played a vital role due to their potential therapeutic action. The curry leaves, Murraya koenigii, and Micromelum minutum are two most common aromatic herbs widespread in Sri Lanka and many other Asian countries. They are rich in nutrition and exert several medicinal properties such as antidiabetic, antioxidant, antimicrobial, anti-inflammatory, and anti-carcinogenic due to various essential phytochemicals, minerals, and trace minerals. In this study, we determined the proximate composition, in vitro antioxidant activity, total phenol (TPC), flavonoid content (TFC), and antibacterial activity in both species using standard methods. Results showed that both species varied greatly in nutritional composition, antioxidant, and antibacterial activities. The nutrient composition in terms of ash, crude protein, and fat was significantly high in M. koenigii based on dry weight basis. In vitro antioxidant potential of M. koenigii and M. minutum was evaluated by means of the DPPH radical scavenging assay, and the IC(50) values of M. koenigii and M. minutum were 107 ± 2 μg/mL and 208 ± 4 μg/mL, respectively. The TPC and TFC of M. koenigii were 101 ± 1 mg GAE/g and 9.75 ± 0.05 mg QE/g, and M. minutum were 80 ± 2 mg GAE/g and 9.16 ± 0.02 mg QE/g respectively. The antibacterial study was assessed against three bacterial strains. The study showed the highest inhibitory activity for M. koenigii and M. minutum against Staphylococcus aureus and Escherichia coli, respectively at 1.0 mg/mL concentration. The study indicated that M. koenigii possessed a significantly high TPC, and TFC correlated with higher antibacterial and antioxidant activity than M. minutum.