Ultrasonic-assisted preparation of rose oil nanoemulsion: Characterization, anti-Escherichia coli activity, and its application in cucumber juice.

In this study, six rose oil nanoemulsions (RONs) were prepared under different ultrasonic power preparation conditions (65w, 91w, 97.5w, 130w, 162.5w, and 195w), naming RON-65w, RON-91w, RON-97.5w, RON-130w, RON-162.5w, RON-195w, respectively. The particle size, and zeta potential revealed that the mean particle size of RONs decreased with the rising of ultrasonic power when RONs were freshly prepared. RONs had storage stability for at least 30 days, and the particle size variations of RON-65w and RON-97.5w were smaller than other RONs. Time-killing assay, minimum inhibitory concentration (MIC), and growth curve analysis revealed that RONs exhibited higher antibacterial activities against Escherichia coli than rose oil (RO). Scanning electron microscopy and bacterial membrane integrity analysis revealed that RO and RONs exerted their antibacterial effect by increasing the permeability of bacterial cells, and the leakage of nucleic acids and protein caused by RONs were higher than RO (p < 0.05). Compared with MIC assay, RON-65w and RON-97.5w exhibited significantly higher antibacterial activities than other RONs in growth curve analysis, and RON-65w led to highest leakage of nucleic acids and protein among all RONs in bacterial membrane integrity analysis (p < 0.05). Thus, the effect of ultrasonic power on antibacterial activity of RONs was more obvious under agitated conditions than static experimental conditions. The results of application experiment indicated that RON-97.5w displayed greater inhibition ability against E.coli than RO in cucumber juice. Based on the results of this study, rose oil nanoemulsions can be applied as natural preservatives in liquid foods to prevent bacteria contamination.