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Abstract The effects of the gas phase surface discharge plasma system with a spray reactor on yeast in 12, 36, and 60°Brix apple juice were evaluated. Results indicated that the number of Zygosaccharomyces rouxii LB cells in 0.5 L of 12°Brix apple juice was reduced by 5.60 log 10 after discharge plasma treatment for 30 min. When the soluble solids content increased from 12 to 60°Brix, yeast inactivation was decreased by 2.55 log 10. After treatment, the pH level of the apple juice only slightly increased, and the titratable acidity and concentration of reducing sugars remained unchanged. The total color differences between the plasma-treated and untreated samples in 12, 36, and 60°Brix apple juice were 9.53, 7.97, and 3.86. Meanwhile, the concentrations of alcohols, esters, aldehydes, and ketones—the main components of volatile compounds showed no significant change (p < 0.05). Industrial relevance Inactivation of microorganisms using nonthermal plasma technology can reduce food costs and minimize changes in food products and is therefore an alternative to heat-based technology. The proposed research showed that the gas phase surface discharge plasma treatment with a spray reactor can effectively reduce Zygosaccharomyces rouxii in apple juice. In addition, the effect of plasma treatment on the color and volatile compounds of the apple juice were determined. This study provided a technical support for the application of plasma technology in apple juice processing. Highlights • Yeast cells were reduced by 3.05–5.60 log 10 after plasma treatment for 30 min. • Increased soluble solids content negatively affected yeast inactivation. • Plasma treatment did not affect titratable acidity and reducing sugar content. • The total color differences in samples were 3.86–9.53 after plasma treatment. • Plasma treatment did not change in volatile compounds, compared with the control. [ABSTRACT FROM AUTHOR]

Cold atmospheric plasma is a promising sterilization technology in the food industry. However, there are only a few studies on the process of inactivating microorganisms in liquids, and it is necessary to establish an efficient prediction model before widespread industrial application. In this study, the commercial software COMSOL was used to establish a gas phase surface discharge plasma reactor simulation model, and experiments were subsequently performed to validate the model. Results showed that increasing the initial concentration of yeast in water has a negative effect on the inactivation process. In contrast, yeast inactivation was not significantly affected by reactor diameter changes from 40 mm to 50 mm. The model showed good fit to the experimental data under various operating conditions, and the value of the parameter associated with the reaction coefficients provided insight into the process. This model can be used for process design and improvement of plasma-inactivated liquid foods. • A coupled gas-liquid mass transfer-inactivation model was developed and validated. • Different voltages were used to verify the prediction effect of the model. • The influence of initial concentration and reactor dimensions was predicted. [ABSTRACT FROM AUTHOR]

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 log 10 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. • Yeast content in apple juice can be inactivated by electrical discharge plasma. • A 5.60-log reduction in yeast can be achieved by an exposure time of 30 min. • Titratable acidity and reducing sugar content did not change upon plasma treatment. • The total colour differences in samples were 2.96–9.77 after plasma treatment. • Electrical discharge plasma treatment can retain volatile compounds in apple juice. [ABSTRACT FROM AUTHOR]