An investigation into the use of plasma activated water to improve the quality and safety of fresh meat

Hot water washing systems, applied separately or in combination with steam pasteurization and the use of chemical disinfectants, such as chlorine and organic acids, are conventionally used in the meat industry to achieve microbial safety and reduce the risk of cross-contamination throughout carcass processing. The application of heat in hot water washes, applied at temperatures greater than 74°C, and steam in steam pasteurization, causes adverse sensory changes particularly in the appearance and texture of treated surfaces. Similarly, organic acid spray washes can lead to discolouration of cut meats. Furthermore, there are growing concerns over the emergence of acid-tolerant and chlorine resistant food borne pathogens as well as concerns over the formation of carcinogenic by-products through reactions between chlorine and organic matter. Novel cold plasma technologies including plasma activated water (PAW), have shown real promise as an alternative and environmentally conscious meat decontamination method. In this study, the effects of plasma activated water on planktonic and adhered cells on beef surfaces and the potential for induced resistance was examined. Additionally, the impact of PAW on quality attributes was also investigated. Results show that PAW generated by a pin-to-plate spark air plasma reduced planktonic cell population of P. fluorescens, L. lactis and B. thermosphacta, E. coli, L. monocytogenes and S. Typhimurium by 0.58, 0.70, 0.57, 0.53, 1.69 and 1.16 log, respectively. PAW’s efficacy was lessened when used to treat adhered cells on beef and lamb. A log reduction of 0.37, 0.40, 0.69 log on beef and a 0.29, 0.19, 1.07 log on lamb was reported for S. Typhimurium, E. coli and L. monocytogenes, respectively. PAWs efficacy is improved through changes in the generation parameters including an increase in initial water conductivity and water activation time. Contact time between PAW and the treated surface was also determined to be a determining factor in PAWs antibacterial activity. Furthermore, the application of warm PAW (35°C and 55°C) significantly reduced bacterial population when compared to PAW applied at room temperature. When applied onto meat surfaces, PAW showed no significant reductions in the nutritional composition of meat including vitamin B6, zinc, iron, selenium and protein. PAW treatment also did not significantly change colour coordinate values of L*, lightness, and b*, redness of beef samples. Furthermore, the extent of lipid oxidation was reduced with PAW treatment compared to water and lactic acid. Therefore, our findings demonstrates that PAW may be a viable meat decontaminant with minimal effect on the desirable quality attributes of meat