Inactivation of Listeria monocytogenes and Escherichia coli O157:H7 inoculated on fresh-cut romaine lettuce by peanut skin extract/benzethonium chloride emulsion washing

Abstract

The aim of this study was to examine the washing effect of the positively charged emulsion produced by the combination of peanut skin extract (PSE) and benzethonium chloride (BEC) against Listeria monocytogenes and Escherichia coli O157:H7 on fresh-cut romaine lettuce. PSE and BEC showed a good washing effect regardless of pathogenic bacteria type. Specifically, the combination of 5 mg/mL PSE and 0.5 mg/mL BEC (PSE-BEC) resulted in 3.06 and 2.83 log reductions in L. monocytogenes and E. coli O157:H7 populations inoculated on romaine lettuce leaves, respectively, compared to washing with water alone. Further, the PSE-BEC treatment-induced reduction in the levels of these two pathogenic bacteria was greater than that with 0.2 mg/mL sodium hypochlorite. SEM analysis revealed a decrease in the number of bacteria and a change in cell membrane morphology on the lettuce surface following PSE-BEC treatment. Moreover, analysis of contact angle and particle characteristics (i.e. ζ–potential, particle size, and polydispersity index) of the washing solution indicated a correlation between the washing effect and the physicochemical characteristics of the PSE-BEC solution. Furthermore, washing with PSE-BEC did not change the quality of lettuce leaves during storage. These results suggest that PSE-BEC has the potential to be used as an effective washing agent for freshly cut romaine lettuce as an alternative to chlorine-based sanitizers.