Antioxidant, antibacterial and tyrosinase inhibiting activities of extracts from Myristica fragrans Houtt

Aims: To evaluate the antioxidant, antibacterial and tyrosinase inhibiting activities of the methanolic extracts of the leaf and fruit pericarp from Myristica fragrans. Study Design: In vitro assays. Place and Duration of Study: School of Biosciences, Taylor’s University (Jan – December 2013) Methodology: Total phenolic content (TPC) was assessed using Folin-Ciocalteu’s method. The antioxidant activity was evaluated via radical scavenging against 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferric ion reducing power (FRP) and ferrous ion chelating (FIC). Antibacterial activity was assessed using disc diffusion on four Gram-positve bacteria: M. luteus, E. faecalis, S. aureus, B. cereus and three Gram-negative bacteria: P. aeruginosa, E. coli and K. pneumoniae, followed by determination of minimum inhibitory concentration and minimum bactericidal concentration using broth dilution assays. Tyrosinase inhibiting activity was assessed using L-3,4-dihydroxyphenylalanine, L-DOPA as the substrate. Results: The methanolic leaf extracts exhibited significantly higher TPC 2712-2779 mg gallic acidequivalent/100 g in contrast to that obtained from the pericarp. The leaf extracts also exhibited significantly stronger DPPH radical scavenging activity (2962-3787 mg ascorbic acid equivalent/100 g), ferric reducing activity (1383-1653 mg gallic acid equivalent/100 g) and chelating activity, as compared to the pericarp extracts. Leaf extracts were effective against all Gram-positve bacteria tested: M. luteus, E. faecalis, S. aureus, B. cereus (minimum inhibitory concentration 250-500 μg/mL; minimum bactericidal concentration 250-500 μg/mL). Studies on the tyrosinase inhibiting properties for applications in preventing food browning or treating hyperpigmentation disorders, showed significantly stronger activities exhibited by the leaf extracts (80-81%) as compared to that shown by pericarp (27-31%). Conclusion: The present results suggest that nutmeg leaf could be employed as a natural antioxidant, antibacterial and tyrosinase inhibiting agent for applications in pharmaceuticals or in functional foods.