Purpose: In response, this study aimed to quantify Listeria monocytogenes transfer during cutting of cantaloupe and honeydew melon as impacted by three different areas of the rind and product temperature.
Methods: Cantaloupes and honeydew melons obtained from a local retailer were washed, immersed for 10 min in a 3-strain avirulent cocktail of L. monocytogenes (strains M3, J22F, and J29H) containing 109 CFU/ml, air-dried for 1 h and then stored at 4 or 30°C for 24 h to simulate processing plant and field conditions, respectively. An 18-mm diameter sterile cork borer was used to obtain five 30 mm-long core samples from the blossom scar, stem scar, and circumference regions. After aseptically cutting each core sample into six 5mm long pieces, the five pieces from the same depths and rind locations were added to 50 ml of phosphate buffer saline, homogenized by stomaching, serially diluted, surface-plated on trypticase soy agar containing 0.6% yeast extract, 0.1% esculin, and 0.05% ferric ammonium citrate and incubated at 37°C for 24 h to enumerate Listeria.
Results: After surface inoculation, the cantaloupe and honeydew melon rinds contained L. monocytogenes populations of 6.81 and 5.67 log CFU/g, respectively. Listeria transfer ranged from 2.89 to 4.31 and 1.48 to 3.15 CFU/g for cantaloupe and honeydew, respectively. Overall, no significant difference in L. monocytogenes transfer was seen at the different depths (P > 0.05). However, transfer was significantly greater in the blossom and stem scar regions of cantaloupes cored at 4°C as compared to 30°C (P < 0.05) with no significant difference observed for the circumference of the rind (P > 0.05). Listeria transfer was also greater for cantaloupe compared to honeydew melon at the stem scar, blossom scar, and circumference (P < 0.05).
Significance: These results demonstrate that L. monocytogenes can be readily transferred from the rind to the interior flesh of cantaloupe and honeydew melon during preparation. Hence, thorough washing with a sanitizer or otherwise treating the rind surface remains critically important to minimize contamination of the edible portions during cutting with these quantitative findings being helpful for current risk assessments.