Purpose: To compare three different sanitizers for the removal of L. monocytogenes from cantaloupe stem scar and netted rind and to determine if infiltration of the pathogen occurs as a result of inoculation or sanitizer treatment.
Methods: Freshly harvested cantaloupes were spot inoculated with L. monocytogenes at the stem scar (6 log) and netted rind (7 log). After overnight acclimation, the melons were subjected to no treatment (control) or an 8-min treatment in 200 ppm chlorine, 3 ppm chlorine dioxide, or 5 % levulinic acid and 2 % sodium dodecyl sulfate (LASDS). Cantaloupes were analyzed on the day of treatment, day 0, after storage at 4°C for 3 and 15 days, and after 8 days stored at 25°C. Two groups of melons were analyzed at each time point, one for surface L. monocytogenes and the other for infiltration of the pathogen into cantaloupe flesh.
Results: Decrease (-) or increase (+) in log CFU/kg values compared to control samples on day 0/day 3/day 15 (* indicates significant difference, P< 0.05) were -0.73/-1.09*/-3.29*; -0.20/+0.22/-0.16; -2.59*/-2.29*/-3.52* (stem scar) and +0.51/-3.29*/-3.50; +1.95/-0.94/-1.71; -2.07*/-6.21*/-2.83 (netted rind) for chlorine, chlorine dioxide, and LASDS, respectively. Infiltration of pathogen was detected via enrichment culture (detection limit 1 CFU/sample) in both treated and non-treated cantaloupe stem scar and netted rind flesh.
Significance: Treating cantaloupes with LASDS led to greater reductions of L. monocytogenes on surface tissues compared to chlorine or chlorine dioxide on the day of sanitizer treatment and for short term storage. Infiltration of L. monocytogenes was more prevalent at the stem scar than at the netted rind and occurred with or without immersion into sanitizer solutions.