Effects of pulsed light and sanitizer wash combination on inactivation of Escherichia coli 0157:H7, microbial loads and apparent quality of spinach leaves

Authors: Mukhopadhyay, Sudarsan; Sokorai, Kimberly; Ukuku, Dike; Fan, Xuetong; Olanya, Modesto; Juneja, Vijay

Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2019
Publication Date: 1/31/2019
Citation: Mukhopadhyay, S., Sokorai, K.J., Ukuku, D.O., Fan, X., Olanya, O.M., Juneja, V.K. 2019. Effects of pulsed light and sanitizer wash combination on inactivation of Escherichia coli 0157:H7, microbial loads and apparent quality of spinach leaves. Food Microbiology. 82:127-134. https://doi.org/10.1016/j.fm.2019.01.022.
DOI: https://doi.org/10.1016/j.fm.2019.01.022

Interpretive Summary: Microbial safety of food continues to be a major concern. Leafy greens like spinach and lettuce have been frequently implicated in outbreaks. Current chlorine based decontamination methods have limited effectiveness. Hence, new decontamination methods are needed. Pulsed light is an effective technique for produce surface decontamination. However, pulsed light generates heat and therefore prolonged exposure to pulsed light can cause quality damage. In this study, we applied pulsed light in combination with a novel sanitizer wash to reduce the exposure time to pulsed light. Result showed that the new pulsed light in combination with active sanitizer wash can reduce 99.999% pathogens like E. coli O157:H7 in spinach without any detrimental effect on its quality.

Technical Abstract: The purpose of this study was to investigate the efficacy of pulsed light (PL), a new formula of sanitizer (HEN) consisting of hydrogen peroxide, EDTA and Nisin, as well as synergy of PL and HEN sanitizer (PL-HEN) wash in inactivating E. coli O157:H7 on spinach. The treatment effect on microbial loads and apparent quality during 13 days storage at 4 deg. C was also determined. A bacterial cocktail containing three strains of E. coli O157:H7 was used as inoculum based on their association with produce-related outbreaks. Spinach leaves were spot-inoculated on surface before treating with PL (1- 63 J/cm2), HEN sanitizer wash (2 min) or their combinations. PL inactivation was in'uenced signi'cantly at low doses. Treatment dose of 15.75 J/cm2, equivalent to 15 s intense PL treatment, was found optimal above which adverse quality effect was evident. The optimal PL dose resulted 2.7 log CFU/g reduction of E. coli O157:H7 while a rapid 2 min wash in sanitizer formulation HEN, provided comparatively low, 1.8 log CFU/g, reduction of the pathogen. Two different sequences of PL and HEN treatment combinations were tested. In PL-HEN treatment, inoculated leaves were first treated at optimal PL dose (15.75 J/cm2) followed by 2 min immersion in HEN whereas in HEN-PL treatment, leaves were first washed in HEN before PL exposure. HEN-PL treatment indicated a compound inactivation activity (4.6 logs reduction) while PL-HEN treatment indicated a strong synergistic inactivation as E. coli cells were not detectable after treatment indicating > 5 log reduction. The PL-HEN treatment not only significantly reduced spoilage microbial populations on spinach but also slowed their growth during storage. Furthermore, the visual and firmness quality of spinach were not significantly affected by the PL-HEN treatment. Overall, our results demonstrate that integrated PL-HEN technology can be used to enhance microbial safety of spinach.