Nonthermal Milk Pasteurization by Continuous-Flow Liquid Phase Plasma Discharge

Raw milk contains many pathogens, including Escherichia coli, Vibriobacterium, and Brucella. If consumed directly without treatment, it will cause symptoms such as vomiting, diarrhea, abdominal pain, and fever, and in severe cases, lead to death. Currently, high temperature/short time pasteurization (HTST), low temperature/long time pasteurization (LTLT), or ultra-high temperature (UHT) sterilization are used to inactivate microbes and enzymes and remove toxic substances. Such processing ensures milk safety but caused loss of 33% thiamine and 50% of vitamin B12 relative to raw milk, decreased vitamin E content, and even inefficient inactivation of heat-resistant pathogens. Therefore, nonthermal milk processing technologies are urgently needed for effective pathogen inactivation and in the meantime better nutrient preservation. Plasma discharge is a promising nonthermal technology that can inactivate microorganisms under milder conditions while meeting microbial safety standards and preserving biologically active compounds critical to milk quality. Compared with thermal pasteurization, plasma disinfection can be faster with lower energy consumption, is environmentally friendly, has a wide range of applications, and is very promising in industrial applications. A novel continuous liquid-phase plasma discharge (CLPD) process for nonthermal and continuous milk processing was evaluated and it was found to inactivate over 6 log CFU total bacteria with 50 ml/min continuous flow rate and 250-watt power. The milk quality was reserved as well as HTST treated raw milk in terms of true protein, lactose, casein, solids, milk urea nitrogen, and pH.