Reduction of Listeria monocytogenes on post-harvest carrot and tomato by radiation, santizer and biocontrol treatments and their combinations

Authors: RODRIGUEZ, ARMARYNETTE - University Of Puerto Rico; Olanya, Modesto; Ukuku, Dike; Niemira, Brendan; ORELLANA, LYNETTE - University Of Puerto Rico; Mukhopadhyay, Sudarsan; Cassidy, Jennifer; Boyd, Glenn

Submitted to: LWT - Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2019
Publication Date: 11/15/2019
Citation: Rodriguez, A.B., Olanya, O.M., Ukuku, D.O., Niemira, B.A., Orellana, L.E., Mukhopadhyay, S., Cassidy, J.M., Boyd, G. 2019. Reduction of Listeria monocytogenes on post-harvest carrot and tomato by radiation, santizer and biocontrol treatments and their combinations. LWT - Food Science and Technology. 118:1-8.
DOI: https://doi.org/10.1016/j.lwt.2019.108805

Interpretive Summary: The lethal effects of non-thermal interventions on pathogenic bacteria may be enhanced by hurdle or combinations of treatments. We investigated the effects of radiation, chemical sanitizer and biocontrol (competitive bacteria), applied against Listeria monocytogenes on post-harvest carrot and tomato, as single or combinations of treatments. Following pathogen inoculations on carrot and tomato, produce was processed immediately (day 0, 20C), or processed after 7 days of storage at either 5C (produce storage) or 20C (room temperature). Treatment effects were evaluated by computing Listeria survival on inoculated produce relative to the untreated produce (control). At 7 days of storage, combinations of radiation (R), sanitizer (S), and biocontrol (B) hurdle treatments (R+S+B) reduced Listeria survival by 2.5-5.0 log CFU/g, while S+R+B reduced Listeria survival by 2.4-5.0 log CFU/g of produce at both temperatures. Single treatments (S, R or B) also reduced Listeria survival on post-harvest produce as the overall treatment efficacies on pathogen survival were sanitizer > radiation > biocontrol. Survival of Listeria on post-harvest carrot and tomato was severely degraded by hurdle treatments, implying that its applications can improve the safety of post-harvest produce.

Technical Abstract: Control of foodborne pathogens on post-harvest produce may be improved by combined treatments. Hurdle applications may enhance the lethal effects of non-thermal interventions and simultaneously reduce treatments for bacteria inactivation. We evaluated the effects of gamma radiation (0.5 kGy), nisin-based sanitizer (100% concentration), and competitive biocontrol microbes (cocktail of non-pathogenic Pseudomonas fluorescens, ~6 logs) on the survival of Listeria monocytogenes on post-harvest tomato and carrot. Produce storage temperatures (5 and 20C) and days (0 and 7), with single, two or three treatment combinations of radiation (R), sanitizer (S) and biocontrol (B) were investigated for pathogen survival. Total bacteria on untreated carrot and tomato were also quantified and ranged from 4.5-5.5 log CFU/g. Significant differences (P<0.05) in L. monocytogenes populations and subsequent pathogen reductions on produce by hurdle treatments were recorded. L. monocytogenes reductions on carrots and tomatoes varied and in hurdle treatments (day 7) combinations of R+S+B and S+R+B treatments reduced Listeria survival by 2.5-5.0 log and 2.4-5.0 log CFU/g of produce, respectively, at both temperatures. The sanitizer (S) treatment (day 7) against Listeria resulted in 2.2-4.7 log reductions on produce while other single treatments (R or B) also reduced Listeria survival on post-harvest produce. The overall treatment efficacies on pathogen survival were sanitizer > radiation > biocontrol. These results suggest that control of Listeria on post-harvest produce may be improved by treatment combinations. Combined treatment applications could enhance the safety of post-harvest carrot and tomato.