Behavior of Listeria innocua on cut cantaloupe during sanitization and refrigerated storage

Outbreaks that have occurred in fresh-cut produce over the last 10 years have caused increasing concern regarding how such products are produced and consumed. Increasing the antimicrobial efficacy of post-harvest and retail processing is crucial to ensure final product safety. The goal of this study was to investigate aqueous sanitization methods against Listeria on fresh-cut cantaloupe and the survival of L. innocua during post-treatment refrigerated storage for 48 h. Inoculated fresh-cut cantaloupe pieces were treated with peracetic acid (PAA, 80 ppm) or chlorine (200 ppm), (compared to water control). Inoculated cantaloupe pieces were treated by spray application of water or aqueous sanitizer (chlorine, PAA, or sequential applications of these) followed by refrigerated storage. Using cultural techniques, L. innocua, yeast and mold, and total aerobic mesophiles were monitored throughout storage. Sanitizer treatments reduced L. innocua populations by less than 0.5 log CFU cm^-2. L. innocua populations increased significantly between 6 and 48 h of refrigerated storage (p=2.85e-5), with a population growth of up to 1.5 log CFU cm^-2. Yeast populations significantly decreased post-treatment followed by a significant increase after 48 h of refrigerated storage (p=0.0). No significant changes in total aerobic mesophiles were observed (pGROTERDAN0.05). Results from scanning electron microscopy suggest that surface characteristics of cut melon discourage the effectiveness of aqueous sanitization due to bacterial attachment occurring inside the pores of the cantaloupe flesh. In order to provide safety assurance of fresh-cut produce produced at large scale, alternative methods for pathogen inactivation should be investigated.