Purpose The purpose of this paper is to determine the antimicrobial compounds extracted from various types of soybean materials; raw soybean, soybean flour and roasted soybean. Bacteria growth inhibition was tested in E.coli and S. aureus by disk diffusion method. Efficiency of antimicrobial activities were compared among the extracted solution. Design/methodology/approach Soybean (Glycine max) isoflavones contain the ability to inhibit the growth of many strains of microorganisms. The solid-liquid extraction, ethanol-hexane extraction, was modified to isolate the inhibitory compounds from the three different types of soybean materials. All crude extracts at various concentrations performed under different extracted solutions (75, 50, 25, 12.5, 6.25 and 3.125 percent) were tested with E. coli. and S. aureus to determine the antimicrobial activities and the minimum inhibition concentration (MIC). Disk diffusion method was chosen to study the antimicrobial activity of isoflavones. Findings Soybean flour extract inhibited the growth of E. coli and S. aureus more effective than roasted soybean and raw soybean, respectively. The MIC of inhibitory compounds extracted from soybean flour was 6.25 percent (0.031 mg/ml), roasted soybean was 25 percent (0.125 mg/ml) and raw soybean was 50 percent (0.250 mg/ml). Crude extracts of soybean flour and roasted soybean showed better results than raw soybean. All the three of extracted soybeans inhibited the growth of E. coli better than S. aureus. Originality/value Ethanol-hexane extraction was successfully used to isolate the antimicrobial compounds from raw soybean, soybean flour and roasted soybean. Comparison of antimicrobial activity showed that soybean flour contained the highest inhibition activity.

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Grapefruit peel essential oil exhibited antioxidant and antibacterial activities attributed to their phenolic and flavonoid compounds. In this study, nanoemulsion of grapefruit peel essential oil and carrageenan was investigated for their antioxidant properties. The oil in water (o/w) emulsion was formulated with 0.5% and 1.0% (w/v) grapefruit peel essential oil and carrageenan. Carrageenan was utilised as an encapsulating agent to decrease volatility of essential oil and increase its stability. The resulting nanoemulsion was characterised using transmission electron microscopes (TEM), ultraviolet–visible (UV–vis) spectrophotometry and Fourier-transform infrared spectroscopy (FTIR). Nanoemulsion formulated with 0.5% grapefruit peel essential oil exhibited strong radical scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH) effects showing the highest half maximal effective concentration value (EC50) at 83.4 ± 1.4 mg l−1 and revealed the highest total phenolic content (80.1 ± 11.8 mg GAE/g) in comparison with 1.0% grapefruit peel essential oil-nanoemulsion and free grapefruit peel essential oil (2.0% w/v). The cytotoxicity of nanoemulsion prepared from grapefruit peel essential oil against HeLa cells also exhibited higher than 90% of cell viability, which was not affected by the formulation of nanoemulsion. The incorporation of grapefruit peel essential oil into nanoemulsion improved its stability while retaining its bioactivity and non-toxicity.