Purpose: The role of cultivar, storage temperature, and site of contamination on the survival and/or growth of Listeria monocytogenes on whole cantaloupes was evaluated.
Methods: ‘Athena’ and ‘Rocky Ford’ cantaloupe cultivars were grown in fields or high tunnels and harvested at half- to full-slip, and stored at 4°C until inoculated. A multi-strain inoculum of L. monocytogenes (6 log CFU/cantaloupe) was spot-inoculated on the rinds or stem-scars of individual melons, and subsequently stored at 4, 10, and 25°C. L. monocytogenes populations on individual cantaloupes at each temperature were determined for up to 15 days. Also, L. monocytogenes was inoculated into rind extracts, and L. monocytogenes populations and aerobic populations of rind extracts determined during storage at 4°C and 25°C for 7 days. A linear model for ANOVA using a factorial mode was used to compare mean bacterial populations.
Results: L. monocytogenes populations on stem-scars of whole cantaloupes stored at 25°C increased by approximately 2 log CFU after one day, and were significantly greater (P<0.05) than those on whole cantaloupes stored at 4°C and 10°C, which did not increase in the same time-frame. L. monocytogenes populations decreased on cantaloupe rinds by 2-4 log CFU after 7 days of storage at all three selected temperatures, and were not significantly different (P>0.05). In rind extracts stored at 25°C, populations of aerobic bacteria increased while those of L. monocytogenes decreased at day 3; however, at 4°C, growth of L. monocytogenes populations were greater than aerobic populations at 7 days. There were no significant differences in L. monocytogenes populations based on cultivar.
Significance: Site of contamination and storage temperature influenced growth and survival of L. monocytogenes on whole cantaloupe surfaces. L. monocytogenes can proliferate on stem-scars of whole cantaloupes.