Antioxidant and antimicrobial activities of the Mizo traditional medicinal plant, Helicia excelsa and chemical investigation on its bioactive metabolites

The study analysed the leaf extract of Helicia excelsa for the antioxidant, antifungal and antibacterial activities, as well as the chemical components. The plant extract contains appreciable amounts of total antioxidant (26.4 mg ascorbic acid equivalent/g), flavonoid (60 mg quercetin equivalent/g) and phenolic (11.7 mg gallic acid equivalent/g) compounds. The half-maximal inhibitory concentration (IC50) against 1,1-Diphenyl-2-picrylhydrazyl (DPPH) was 17.79± 0.64 µg/mL. It also showed concentration-dependent antioxidant activity by ferric reduction assay. It was effective against fungal species including Fusarium solani, F. keratoplasticum, F. oxysporum and Pyricularia oryzae, showing best activity against P. oryzae. It exerted antibacterial activity against both Gram-negative and Gram-positive species with highest efficacy against Pseudomonas aeruginosa and Bacillus cereus. The minimum inhibitory concentrations were 7.81 mg/mL for B. cereus, B. subtilis, Klebsiella pneumoniae and Salmonella typhimurium; while it was 15.63 mg/mL for P. aeruginosa and Staphylococcus aureus. MBC/MIC ratio showed that the plant extract exhibited bactericidal effects against B. cereus, B. subtilis, P. aeruginosa and S. aureus and bacteriostatic effects against K. pneumoniae and S. typhimurium. Alkaloids, flavonoids, phenols, carbohydrates, glycosides, saponins, proteins and amino acids and phytosterols were detected as the major secondary metabolites. 3-O-methyl-d-glucose was identified as the principle bioactive compound. The findings substantiate H. excelsa as an important medicinal plant that could be a potential source of pharmacologically useful molecules.