Evaluation of Cold Plasma on Physicochemical Properties of Rose Water

IntroductionRose water, as one of the distillation products prepared from the rose, is widely used in the food industry and traditional medicine in Iran. Therefore, maintaining the microbial and chemical quality of this product is important. Non-thermal processing technologies have attracted wide attention from the food industry. These alternative technologies can increase shelf life and reduce the negative impact on nutrients and natural flavor of foods. Cold plasma technology has been used as a replacement for new generation methods and as a non-thermal technology in the food processing. This research was designed to investigate the effect of atmospheric pressure cold plasma on the physicochemical properties and microbial load of rose water. Materials and MethodsIn this experimental research, a dielectric barrier discharge system was designed. This system was used by producing plasma microbubbles to have an effect on rose water samples with an essential oil content of 28 mg/100 ml. Rose water samples were plasma-treated at 12 and 15 kV for 4, 6 and 8 minutes. Tthe essential oil amount, acid value, iodine number, pH, density, oxidation number, ester number and the total bacterial count were then performed on the samples.Results and DiscussionPlasma showed no significant change in the density of rose water in all treatments. Changes in acidity, pH, ester number and iodide number were observed with increasing time and plasma voltage. These changes were significant between the treatment groups and the control group (P<0.05), but not significant within the treatment groups (P<0.05). The greatest decrease in the amount of essential oil was 10.81 and 8.49 mg per 100 ml of rose water, respectively, related to the treatment with voltage of 15 kV at 6 and 8 minutes. Generation/destruction paths of the radicals and their reactions demonstrate the complicated interplay between the plasma induced species (electrons, photons, radicals, etc.) and the dissolved compounds in the liquid species, which ultimately affect the ion concentration (pH and σ) and the oxidizer concentration (redox) in the liquid. However, a decrease in pH is accompanied by an increase in Eh and σ, with a parallel increase in ROS. In addition, plasma in 8 minutes at voltages of 12 and 15 kV caused a decrease of about 3 log in the total number of mesophilic bacteria compared to the control group. Plasma significantly reduced the total number of mesophilic bacteria in rose water. The bactericidal activity of plasma might occur through several mechanisms. Impact on permeabilisation of the cell membrane or wall, leading to leakage of cellular components, containing potassium, nucleic acid, and proteins. In addition, it causes critical damage of intracellular proteins from oxidative or nitrosative species and direct chemical DNA damage. Plasma-generated reactive species and specially H2O2 were found to be the causative agent of cell death. H2O2 is a well-known antibacterial agent that damages iron–sulphur and mononuclear iron enzymes in bacterial cells.ConclusionThe application of plasma at high voltage and longtime caused a sharp decrease in the amount of essential oil, increased acidity and decreased pH of rose water. It is suggested that future studies be conducted on the type of gas used to produce plasma, the size of the reactor used, and the identification of changes in essential oil compounds using gas chromatography with mass spectrometry.Funding Sources This research did not receive any specific funding from funding organizations in the public, commercial or non-profit sectors. Acknowledgement The present research is derived from the master's thesis in physics, and therefore the support of the research deputy of Kashan University and Kashan University of Medical Sciences is acknowledged and thanked.