Efficacy of DBD Plasma Generator with Different Shapes and Materials of Electrodes for Reducing the Microbial Contamination of Herb Powder

Abstract

This paper studies the efficacy of a dielectric barrier discharge (DBD) plasma generator with circular and square electrodes with stainless steel and copper materials in the reduction of microbial contamination in herbs. Four types of electrodes are used: copper and stainless-steel square electrodes of the size 110×110 mm2 and circular electrodes with a 94 mm diameter. The voltage supplied to plasma generator varies between 5 - 15 kV and the frequency is between 1 - 7 kHz. Licorice (Glycyrrhiza glabra Linn.) and sappan tree (Ceasalpinia sappan Linn.) herb powders were packed in polyethylene bags of the size 89×89 mm2 and tested for microbial contamination before and after the plasma irradiation. The samples were treated with plasma for 5, 10, 15, 20, 25 and 30 min. The results indicated that plasma treatment of 30 min is the most effective time for reducing in the aerobic plate count and yeast and mold count of licorice herb powder. This plasma treatment condition effectively reduced initial the aerobic plate count and yeast and mold count from 8.00×104 to 1.30×103 CFU/g and 4.20×102 to 8.0×10 CFU/g, respectively. Escherichia coli were not founded in the control sample and plasma treatment samples (MPN/g < 3.0). The results revealed that plasma treatment reduced microbial contamination to acceptable levels in herb seasoning as indicated in TCP 1380/2550. In sappan tree powder, plasma irradiation also effectively reduced artificially contaminated of Bacillus subtilis in sappan herb.