Finding effective plasma process factors on yeast deactivation by numerical simulation and RSM

In recent years, there has been an increasing interest in the application of plasma technology in food preservation technologies. Plasma is nonthermal physical processing that has a high potential in the field of  food processing. In this study, a mathematical model was investigated for yeast deactivation during plasma treatment. The definitive screen design was used to investigate the factors that affect yeast deactivation by plasma. Four factors of voltage (A: 20- 30 kV), Vessel diameter (B: 40- 60 mm), process temperature (C: 20- 40ºC), and type of plasma media (air or water) were selected. Then the treatment was simulated by COMSOL software. The responses of reaction kinetics coefficient, the ozone concentration, and final deactivation time were analyzed by definitive screen design expert to find the effective model parameters and process optimization. The results show that plasma treatment in water can have the strongest effect than air plasma. The changes in the number of microorganisms have a linear relationship with process time at different voltage- temperature conditions, but the ozone concentration dramatically changes at different combinations of voltage and temperature. The analyzed data show the kreac is affected significantly by the diameter of the vessel and the 221 types of process media (water or air). The ozone concentration only depends on the type of plasma media and the final 223 process time significantly depends on vessel diameter and type of media. Also, in plasma treatment, media type had a significant effect on all 3 responses, while the effect of temperature was only on final process time. For example, at temperature 20ºC the ozone concentration decreased at the first time of treatment and then stay constant, but at 30ºC, the ozone production increased with treatment time. This study showed when an RSM design was applied for designing the experiment which considers different process factors, the results can significantly differ from the study on only one-factor. In plasma treatment, media type had a significant effect on all 3 responses, while the temperature shows its effect only on final process time. Thus it can be concluded that with proper selecting of plasma media, this technology can be used for deactivation of food microorganisms