Nonthermal milk processing and quality preservation by continuous liquid plasma discharge process

Continuous liquid plasma discharge (CLPD) is a promising non-thermal technology that can inactivate microorganisms under milder conditions while meeting microbiological safety standards and preserving bioactive compounds critical to milk quality and composition. The inactivation of pathogenic bacteria in milk using CLPD technology while focusing on its inactivation capacity, maintenance of milk nutrition, and energy efficiency of the inactivation process are being revealed in this study. The liquid-phase plasma treatment system is designed and developed to treat and process raw milk for continuous processing with extremely short processing times lower than 5 milliseconds. In addition, the effect of continuous liquid phase plasma discharge (CLPD) on the inactivation of typical pathogenic E.coli was evaluated according to the controlled operating parameters such as gas type, gas flow rate, milk flow rate, and power usage. For the next step, two CLPD reactors connected in-series were used to achieve double flow rate, and possible future industrialized treatment conditions were evaluated. The optimization of the CLPD process based on at least 6 log inactivation of the target flora with minimum energy input and maximum milk quality retention were optimized by modeling with a response surface approach through a central composite design. When the system liquid flow rate is 50ml/min and the system power supply is 250w, the total number of colonies in raw milk treated with CLPD is 1 or 0 CFU/mL, which meets the regulatory level of 20,000/mL stipulated by the FDA Class A PMO. At the same time, the nutritional content of milk is almost the same as that of raw milk in terms of true protein, lactose, casein, solids, milk urea nitrogen, and pH. These results suggest that the CLPD technology can be developed for effective and efficient milk processing to obtain products that meet FDA PMO safety standards and improve nutritional quality for human health.