Inactivation of yeast in apple juice using gas-phase surface discharge plasma treatment with a spray reactor

Non-thermal plasma technology can inactivate microorganisms that maybe used in the food processing industry. This study mainly aims to evaluate the effect of a gas-phase surface discharge plasma system with a spray reactor on yeasts (Zygosaccharomyces rouxii LB and 1130) in apple juice. This method avoids the limitation of liquid penetration depths in plasma treatment, expanding the processing capacity. Owing to this advantage, this approach can be used to industrialize liquid food sterilization. Experimental results showed that the number of Z. rouxii LB and 1130 cells decreased by about 6.58 and 6.82 log reductions, respectively, in apple juice after discharge plasma treatment for 30 min. The treatment used a voltage of 21.3 kV and inactivation followed the downward concave Weibull kinetics. Longer plasma exposure times with higher discharge voltages and regulated volume flow rate for both gas and liquid phases resulted in greater inactivation rates. Scanning electron microscopy revealed that the structures of plasma-treated cells were severely damaged during the discharge plasma process. Plasma-generated compounds in liquid, such as hydrogen peroxide and ozone in the liquid phase, are generally responsible for the inactivation of microorganisms.