Pilot-scale plasma activated water treatment for decontaminating romaine lettuce and steamed rice cakes

Abstract

The study investigated the effects of pilot-scale plasma activated water (PAW) on the inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes, and indigenous mesophilic aerobic bacteria on romaine lettuce and steamed rice cake (SRC). PAW treatment was conducted by stirring 25 g of romaine lettuce and 80 g of SRC for 20–40 min at 195 rpm in 1 L of PAW, prepared by treating sterile distilled water with surface dielectric barrier discharge for 40 or 60 min. The microbial inactivation rates of foodborne pathogens and indigenous mesophilic aerobic bacteria ranged from 1.3 to 2.5 log on romaine lettuce and SRC, along with PAW generation time (P < 0.05). Inactivation rates of PAW generation time or treatment time against romaine lettuce and SRC were significantly different to the inactivation of distilled water treatments, respectively (P < 0.05). The pH, electrical conductivity, and hydrogen ion concentration correlated with nitrite and nitrate concentrations of PAW prepared at various PAW generation time. In situ pilot-scale PAW treatment also extended the shelf life of the romaine lettuce. The study demonstrates the feasibility of the pilot-scale PAW treatment to improve microbiological safety and its suitability of applying PAW to manufacture romaine lettuce and SRC products.