Indirect Treatment Effects of Water–Air MHCD Jet on the Inactivation of Penicillium Digitatum Suspension

To study whether water-air plasma jets are conducive to improve the inactivation efficacy when the jet does not contact the pathogens directly, in this paper, a water-air micro hollow cathode discharge device is designed and used to inactivate the P. digitatum suspension. The results showed that water vapor added into the working gas can be favorable for the inactivation efficacy. The maximum of the germination inhibition rate reached up to 91%. The content of ·OH and H
₂
O
₂
was also detected by the optical emission spectroscopy and electrochemical measurement technology, respectively. It was found that with the increase in water vapor ratio, the ·OH and H
₂
O
₂
contents increased. The concentration of H
₂
O
₂
produced by the jet in 3 mL phosphate buffer saline buffer ranged from 0.38875 to 3.08089 μmol/L. After treatment, P. digitatum suspension presented strong acidity, which strengthened the inactivation efficiency of H
₂
O
₂
. Even though water mixed with the working gas was not beneficial to the enhancement of acidity, the rule of inactivation efficacy followed the change of H
₂
O
₂
content under synergistic effects of both strong acidity and H
₂
O
₂
. This is one of the possible reasons to improve the inactivation efficacy of the P. digitatum suspension by water-air plasma jets. And the properties of the water-air jets were also studied, such as temperature. When the flow rate was 150 L/h and the distance from the nozzle was 4 mm, the temperature ranged from 24.7 °C to 39.4 °C. The results showed that the more water vapor in the working gas, the higher the temperature of the jet was, but the temperature was low enough for many practical applications. It is proved that even though the plasma jet does not contact the P. digitatum suspension directly, the method that adding water into the working gas of plasma jet is useful to improve the inactivation efficacy.