Effects of direct and in-package pulsed light treatment on inactivation of E. coli O157:H7 and reduction of microbial loads in romaine lettuce

Authors: Mukhopadhyay, Sudarsan; SOKROAI, KIMBERLY - US Department Of Agriculture (USDA); Jin, Zhonglin; Fan, Xuetong; Ukuku, Dike; Olanya, Modesto; LENG, JUNCAI - Tianjin University Of Science And Technology; Juneja, Vijay

Submitted to: LWT - Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2020
Publication Date: 3/1/2021
Citation: Mukhopadhyay, S., Sokroai, K., Jin, Z.T., Fan, X., Ukuku, D.O., Olanya, O.M., Leng, J., Juneja, V.K. 2021. Effects of direct and in-package pulsed light treatment on inactivation of E. coli O157:H7 and reduction of microbial loads in romaine lettuce. LWT - Food Science and Technology. https://doi.org/10.1016/j.lwt.2020.110710.
DOI: https://doi.org/10.1016/j.lwt.2020.110710

Interpretive Summary: The microbial safety of fresh produce continues to be a real concern. Post-processing contamination is a major contributing factor to foodborne illness outbreaks. In the current year of 2020, major multistate outbreaks of Salmonella Javiana and E. coli infections were linked to cut fruits and chopped salad kits as reported by CDC and PHAC. Safe and effective methods are needed to minimize the spread of human pathogen contamination. We have developed an in package high intensity pulsed light treatment that can penetrate plastic packing enclosure and kill the pathogens like E coli O157:H7 on the surface of romaine lettuce. This in-package pulsed light processing can eliminate or at least minimize post processing contamination of romaine lettuce. Thus far the technology has been tested with romaine lettuce as a model produce. The technology needs to be tested using other fruits and vegetables and large-scale studies are needed for validation and future market application.

Technical Abstract: The objective of this research was to develop and evaluate the effects of direct and in-package pulsed light (PL) treatment on the survival of E. coli O157:H7 in Romaine lettuce. Treatment influence on reduction of background microbial loads of Romaine lettuce was also explored. A three strain-cocktail of E. coli O157:H7 was selected for inoculum preparation for their link with foodborne outbreaks. Surface inoculated Romaine lettuce pieces (2.5 x 2.5 cm) was subjected to pulsed light treatment for a maximum of 1 min (63 J/sq.cm). Polyethylene (PE) films of 1, 2 and 3 mils thickness with ample UV transmission (54 - 83%) ability were used for packaging. PL treatment of 10 s, equivalent to a dose of 10.5 J/ sq.cm, was considered optimum beyond which wilting of leaves was observed. Both direct and in-package treatment provided greater than 1 log reduction of the pathogen in 1 s (1.05 J/cm2). Direct treatment resulted in 3.05 to 2.31log CFU/g reduction of E. coli O157:H7 at optimal dose, whereas log reductions were decreased to 2.71- 2.33, 2.65-1.97 and 2.43-1.93 log CFU/g for lettuce in 1, 2 and 3 mil thickness packaging enclosures respectively. The decrease in log reductions was not significantly (P > 0.05) affected by film thickness. No significant difference (P > 0.05) in E. coli O157:H7 decontamination efficacy between packaged and unpackaged Romaine lettuce was observed due to PL treatment. The initial total aerobic bacteria and mold and yeast populations were also reduced significantly by greater than 1 log, due to the treatment. Overall, the results of this work demonstrate that PL treatment may be used to enhance microbial safety and reduce post processing contamination of packaged Romaine lettuce.