Purpose: The purpose of this study was to evaluate the antimicrobial efficacy of a novel commercial naturally-occurring citrus-based sanitizer for preventing cross-contamination of USDA-certified organic cantaloupes during post-harvest washing.
Methods: A 5 strain cocktail of Listeria monocytogenes (LM) resistant to nalidixic acid (NAR) was prepared. A microbroth dilution assay was used to determine the minimum inhibitory concentration (MIC) of the commercial sanitizer (CX; Citrox, Middlesborough, UK) against LM. Wild type (WT) and NAR strains were compared to confirm resistance to CX. Cantaloupe samples were inoculated with LM and placed in solutions of 0%, 0.5%, 0.75% CX (v/v), or 200-ppm chlorine, with or without 2.0% organic load (OL). To determine if cross-contamination occurred in treatment liquids, un-inoculated cantaloupe was introduced to the same solutions after the inoculated samples. After sanitizing, all samples were removed and hand-massaged. The rinsate was plated TSA + nalidixic acid + 0.6% Yeast Extract to enumerate survivors.
Results: The MIC for all WT and NAR LM was 0.5% CX. For the initial sampling, 0.5% CX and chlorine solutions reduced survival of LM by 1 log (90%). For un-inoculated produce, cross-contamination by LM was eliminated both by CX and chlorine compared to the control (ca. 6 to 7 log CFU/g). OL had a negative effect on CX and chlorine inactivation, except for 0.75% CX.
Significance: Results indicate that 0.75% CX had efficacy in eliminating cross-contamination on organic produce even in the presence of OL in a model wash system.