Application of electrical discharge plasma on the inactivation of Zygosaccharomyces rouxii in apple juice

Abstract

Zygosaccharomyces rouxii is an osmotolerant yeast responsible for the quality degradation of apple juices. Cold plasma is a promising method for microbial inactivation. The primary purpose of this work was to study the influence of electrical discharge plasma treatment on hypertonic yeast inactivation in apple juice. The gas-phase surface discharge was triggered along a quartz tube in an electrical discharge plasma system, and then highly reactive species were bubbled into commercial apple juice artificially inoculated with yeast. The results showed that the yeast in the apple juice reached a 5.6 log10 reduction after the plasma exposure for 30 min at a 21 kV discharge voltage. Scanning electron microscopy showed that cell structure was damaged during plasma treatment. Plasma treatment caused a slight increase in pH, while the total soluble solids, titration acidity, and reducing sugar did not significantly change. After treatment, the apple juice brightness and hue values increased, the colour became yellower and lighter, and the main components of volatile compounds did not change significantly (p < 0.05). Plasma treatment can inactivate hypertonic yeast while maintaining the physicochemical properties of apple juice, including the retention of the volatile compounds in apple juice.