OPTIMIZATION OF COLD PLASMA TREATMENT FOR MICROBIAL DECONTAMINATION IN LICORICE (GLYCYRRHIZA GLABRA L.) AS A MEDICINAL PLANT

The cold plasma treatment is a novel, non-thermal, and environmentally safe technique to reduce the microbial population of pathogenic microorganisms in various food packaging materials and agriculture products. This research investigated the effect of cold plasma treatment on the microbial population of licorice (Glycyrrhiza glabra L.). Samples of licorice root were treated with cold plasma in different conditions. The effect of main variables such as energy generator, power, exposure time, pressure, temperature, injected gas, frequency, and the amount of injected gas was optimized. Also, the effect of cold plasma on the glycyrrhizic acid in samples at the highest cold plasma level was studied. The results illustrated that cold plasma technology reduced the undesirable biological contamination in the treated samples. In the current study, the lowest microbial population in treated samples was shown in conditions with cold-vacuumed plasma systems, pressure at 10-2 TORR, injected gas with oxygen and argon (60 L/min), radio frequency energy (RF) with a frequency of 13.56 MHz, exposure time of 3 min, the temperature at 30oC, and power of 100w. This treatment had high efficiency in microbial population reduction and growth inhibition, with 69.6% and 97.38%, respectively. Also, the results of HPLC methods demonstrated that there were not any significant differences between the glycyrrhizic acid of the control sample and cold-plasma-treated samples. The results of this study indicate that cold plasma technology can be used as an important antibacterial method for medicinal plants to reduce microbial population and minimize food quality losses.