Polyphenol composition and antimicrobial activity of various solvent extracts from different plant parts of Moringa oleifera

The extracts of Moringa oleifera, a traditional medicinal and culinary plant containing phytochemicals with diverse therapeutic properties were investigated. Five parts of the plant were extracted with 5 different solvents to analyze the total phenolics content (TPC) and total flavonoids content (TFC) which were then tested for their antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging, reducing potential, and total antioxidant capacity assays. The TPC-TFC were highest in leaves. TPC in ethyl acetate extract (200 ± 10 mg/g) and TFC in aqueous extract (69 ± 3 mg/g) were the highest. The antioxidant activity was highest in the leaves when compared with other parts like roots, barks, and flowers. Many phenolic compounds were quantified using UHPLC, the flavonols and hydroxybenzoic acids were dominant in the leaves, roots, barks, flowers and seeds. Myricetin (1530 ± 10 µg/g) and quercetin (985 ± 4 µg/g) in leaves along with gentisic acid (85 ± 2 µg/g) and biochanin A (45 ± 1 µg/g) in the roots were considerably higher than other phenolic components found in other parts of the plant. The antibacterial activity of methanol, ethanol, and ethyl acetate leaves extracts showed larger zones of inhibition against Pseudomonas aeruginosa than Erwinia carotovora. Using minimum inhibitory concentration (MIC), the growth inhibition of P. aeruginosa and E. carotovora were found to be 86 ± 1% (ethyl acetate extracts of roots) and 79 ± 0.3% (ethanolic extracts of leaves), respectively. These results suggested that ethyl acetate, ethanol, and methanol extracts might provide the highest amount of potentially beneficial compounds that may be helpful in treating some diseases.