Melinjo (Gnetum gnemon L.) is a native plant in Indonesia. Melinjo peel is generally disposed of, although it contains tannin, flavonoid and saponin, which can be used as antimicrobial compounds. The purpose of this research was to analyze the antimicrobial activity of melinjo peel extract. Maceration method was conducted to extract the melinjo peel, using ethyl acetate as the solvent. The extract at concentration of 4, 8, 12, and 16% (w/v) could inhibit Escherichia coli ATCC 8739, Bacillus cereus ATCC 10876, and Pseudomonas aeruginosa ATCC 9027, but could not inhibit Rhizopus oligosporus ATCC 22959. The extract MIC and MBC value was ranged from 0.50-0.69% and 2.00-2.76%, respectively. Alkaloids, saponin, phenolic, flavonoids and glycosides were found in the extract. The inhibition of selected extract (12%) had a similar level to 1000 ppm Colistin against E. coli and P. aeruginosa. Low pH (pH 4) increased the inhibition of the extract, while neutral pH decreased the inhibition. Heating extract at 65 0 C for 30 minutes increased the inhibition, whereas heating at 75, 85, and 95 0 C decreased the inhibition. The present of salt and sugar at concentration of 1-5% and 10-50%, respectively, increased the inhibition. The extract could damage cell morphology and was confirmed by the presence of ions (Ca 2+ , K + , dan Mg 2+) outside of the cells.

Melinjo (GnetumgnemonL.) is a typical Indonesian plant that has many benefits such as antimicrobial agent. The aim of this study was to determine the antimicrobial activity of red melinjo peel extract. In this study, extraction was conducted by maceration using ethyl acetate as solvent for 24 hours at room temperature. 4-16% red melinjo peel extract (w/v) could inhibit the growth of Staphylococcus aureusATCC 6538, Listeria monocytogenesATCC 7644 and SalmonellaTyphi ATCC 14028. However 4-16% red melinjo peel extract could not inhibit the growth of Candida albicansATCC 10231. In stability test, the selected extract had a stable inhibition at pH 4-7, heat treatment 65oC-95oC for 30 minutes, salt 1%-5%, and sugar 10%-50%. The selected extract produced the biggest inhibition diameter at low pH (pH 4) and produced the smallest inhibition diameter at neutral pH (pH 7). Heat treatment 65oC for 30 minutes produced the biggest inhibition diameter among tested bacteria and decreased with increasing heating temperature. Addition of 1-5% NaCl and 10-50% sucrose worked synergistically with the selected extract in inhibit the growth of the tested bacteria.