Purpose: To evaluate the survival of various strains of L. monocytogenes, L. innocua and Salmonella enterica on watermelon surfaces under varying conditions of storage temperature and pathogen dose as well as their persistence after post-harvest processing including washing and disinfection.
Methods: The effect of storage conditions (15 to 37°C for up to 10 days) on the survival of Listeria spp. and Salmonella at various inoculation doses (log 1 to log 6 CFU/cm2) was evaluated on watermelon upper rind exterior and the yellow ground spot following a factorial design. Additionally, disinfection by total immersion or swabbing in commercial solutions of sodium hypochlorite and peracetic acid were evaluated to determine the log-reduction of Listeria spp. on watermelon rinds following attachment.
Results: Immediate drop in population densities was determined for Listeria and Salmonella within the first 24 h and persistent viability was highly dependent on storage temperature and inoculum dose (P < 0.05), however loss of viability after 10 d was substantial at temperatures greater than 20°C. The behavior of L. monocytogenes in comparison to L. innocua or Salmonella was not significant (P > 0.05) thus L. innocua was judged to be an acceptable surrogate for rind survival under BSL 1 conditions. Population behavior was not different between the upper rind and the yellow ground spot. Disinfection by immersion in 30 mg/l peracetic acid or 100 mg/l of sodium hypochlorite products resulted in 2-2.5 log-reduction of attached cells.
Significance: Persistence of L. monocytogenes on watermelon could represent a risk for food safety, however proper handling and effective postharvest washing could be implemented as preventive control strategies and achieve significant risk reduction.