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Inactivation of yeast by dielectric barrier discharge (DBD) plasma in helium at atmospheric pressure

To reveal the inactivation mechanism of microorganism in plasmas, a baker's yeast (Saccharomyces cerevisiae) sample is exposed in dielectric barrier discharge plasma in helium at atmospheric pressure. The mitochondrial activity charactering the survival probability of the yeast cell is measured by the 3-(4, 5-dimethylthiazol-2-yl) 2, 5-diphenyl-tetrazolium bromide method. The results show that the survival probability of yeast cells sharply decreases within the exposure time of 1.0-2.5 min and almost remains constant as exposure time is longer than 2.5min. The increase of the protein concentration in the supernatant solution of yeast suspension indicates that the intracellular proteins leak to the extracellular environment when the cells undergo plasma exposure, and gross structural damage is observed by a scanning electron microscope. The possible cause of the rupture is the electrostatic tension produced by the charges accumulated on the cell surface in the plasma. In addition, the extracellular medium whose pH is changed may also contribute to the rupture of the treated yeast cells.