Antibacterial and antioxidant activities, phytochemical and toxicity analyses of Melinjo (Gnetum gnemon L.) leaf extract

Global concern about foodborne pathogens is heightened due to their potential to cause widespread illness, economic loss, and worldwide undermining of food safety and security measures. Plant-derived antimicrobial compounds typically have a wider range of efficacy against foodborne pathogens than synthetic alternatives, in addition to being biodegradable and eco-friendly. Incorporating natural antimicrobial agents is crucial to mitigate the threat of antimicrobial resistance, promote sustainable practices, and lessen the possible adverse effects linked to synthetic substances. Melinjo (Gnetum gnemon L.) is one of the possible plant options. In Malaysia and Indonesia, several parts of the Melinjo plant, including leaves, seeds, and fruits, are utilized in culinary practices. The antibacterial activities of ethanolic Melinjo leaf extract were determined using standard methods of CLSI, in terms of well diffusion assay (WDA). minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and time-kill analysis. Total phenolic content (TPC) and antioxidant activities were performed using 2,2-diphenyl-1-picrylhydryzyl (DPPH) assay, ferric reducing antioxidant power (FRAP) assay and 2,2'-azino-bis(3- ethylbenzothiazoline-6-sulfonic acid (ABTS) assay. Melinjo showed antibacterial activities against tested foodborne bacteria. The inhibition zone in WDA ranged from 8.50 to 13.50 mm, MIC ranged from 6.25 to 50.00 mg/mL and MBC values were between 12.5 to >50 mg/mL. Results from time-kill analysis showed that at 4×MIC bacterial strains were completely killed within 1 to 4 h incubation time. Total phenolic content was demonstrated at 39.4 ± 2.69 mg GAE/g, and DPPH and ABTS assay showed scavenging activity with the IC50 value of 2.51 ± 0.26 mg/mL and 5.02 ± 0.30 mg/mL, respectively. Ferric-reducing antioxidant power activity was determined at 696.67 ± 13.56 μmol TEAC/g DW. The LC-MS analysis revealed the presence of various nonvolatile compounds like anonaine, diosmetin 7-rutinoside, rhapontigenin, hamamelitannin, heteroflavanone C, tryptophan, [10]-gingerdiol. GC-MS analysis identified several volatile compounds such as phytol, vitamin E, ascorbic acid 2,6-dihexadecanoate, linoleic acid, gamma-sitosterol, and gamma-tocopherol. These identified compounds may have contributed to the antibacterial and antioxidant activities of Melinjo leaf extract. The LC50 of leaf extract was found to be 41.08 mg/mL which is more than 1 mg/mL; meaning that the extract is non-toxic and safe for human consumption. In conclusion, ethanolic Melinjo leaf extract exhibits antibacterial activities against selected foodborne bacteria, and antioxidant potential due to the presence of bioactive compounds. It also is safe for consumption. Therefore, ethanolic G. gnemon L. extract leaf extract can be established as a natural anti-bacterial agent to be used in the development of natural food preservatives.

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