Antimicrobial activity of eight plant essential oils having antioxidant property against spoilage microbes.

Aims: To identify efficient, broad-spectrum, and non-toxic preservatives for natural agricultural products, eight essential oils were screened for high inhibitory and antioxidant activities against spoilage microbes.

Methods and results: The zone of inhibition test and minimum inhibitory concentration (MIC) assay were performed to assess the antimicrobial activity of eight essential oils against Bacillus subtilis, Staphylococcus aureus, Penicillium, Saccharomyces, and Escherichia coli. Among the eight essential oils, garlic and rose essential oils exhibited the best inhibitory effects, their MICs against the spoilage microbes were 40-640 μl/l and 10-320 μl/l, respectively. In addition, the antioxidant activities of eight essential oils were compared using the DPPH and ABTS radical-scavenging assays and the reducing power assay. Eight essential oils had antioxidant capacity, among which rosemary, thyme, rose, and tea tree essential oils performed the best. Moreover, the combination of thyme and rose exerted stronger antioxidant activity. Therefore, the concentrations of rose and garlic, and thyme essential oils were optimized using response surface methodology to obtain the optimal composite ratios, which were 1254 μl/l, 640 μl/l, and 1228 μl/l for rose, garlic, and thyme, respectively. The DPPH free radical-scavenging rate detected using this formulation was 50.2%, basically consistent with the prediction. Zone of inhibition diameters with the compound essential oil, against five spoilage microbes, were all greater than 45 mm.

Conclusions: The essential oil combination had high antimicrobial, against agricultural product spoilage microbes, and antioxidant activities.