Combined Effect of Cold Plasma and UV-C Against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on Fresh-cut Lettuce
This study was conducted to investigate the effect of cold plasma combined with UV-C irradiation against Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes on lettuce. E. coli O157:H7, S. Typhimurium, and L. monocytogenes, corresponding to approximately 5.82, 5.09, 5.65 log CFU/ g, were inoculated on lettuce, respectively. Then, the lettuce was treated with cold plasma, UV-C and combination (cold plasma + UV-C), respectively. The treated lettuce was stored for 9 days at 4oC for microbiological analysis and sensory evaluation. Cold plasma reduced the populations of E. coli O157:H7, S. Typhimurium, and L. monocytogenes by 0.26, 0.65, and 0.93 log CFU/g, respectively. Each microorganism were reduced by 0.87, 0.88, and 1.14 log CFU/ g after UV-C treatment. And, the combined treatment that was treated by cold plasma after UV-C treatment reduced the populations of inoculated microorganisms by 1.44, 2.70, 1.62 log CFU/g, respectively. The all treatment significantly (p < 0.05) reduced the populations of all inoculated bacteria compared to untreated lettuce. UV-C combined with cold plasma was the most effective for reducing the pathogenic bacteria on lettuce, by showing log-reductions of ≥ 2.0 log CFU/g. All treatment was not significantly different until 6 day storage compared to control group in terms of appearance, texture and overall acceptability. Therefore, the combined treatment will be an effective intervention method to control the bacteria on lettuce.