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Atmospheric cold plasma is a powerful and profitable microbial decontamination technology in the food industry. The microbial load and food matrix have a great influence on the plasma inactivation effect. This study aimed to quantify the effects of initial cell concentration and soluble solids on the inactivation of yeast in apple juice by gas-phase surface discharge plasma. A computer simulation model was developed to predict the inactivation process using commercial finite element software, COMSOL Multiphysics, and the model was verified by experiments. Studies have shown that the inactivation of yeast was affected by the initial cell concentration and soluble solids. These effects were quantified by fitting equations and used as model inputs. The simulation model predicted the D-value of plasma inactivation of yeast under different discharge voltages and apple juice volume, which was verified in experiments. Therefore, the established model can be used for plasma development to predict how the food matrix affects the inactivation process, thereby providing useful and practical tools for amplifying the commercial application of plasma. • A surface discharge voltage plasma deactivation model was developed and verified. • Model correlated the cell concentration and soluble solids with inactivation rates. • The influence of discharge voltage and process capacity was predicted in the model. [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]