Inactivation of Aerobic Mesophilic Bacteria and Escherichia coli K-12 on Cantaloupe Rind Surface Using Wet Steam Treatments

Introduction: The presence of human bacterial pathogens on cantaloupe rind surfaces and transfer to fresh-cut pieces during preparation continue to be a microbial safety hazard for the produce industries and consumers alike.

Purpose: A prototype flash steam lab unit was used to treat cantaloupe rind surfaces inoculated with Escherichia coli K-12 bacteria at 5.2 log CFU/cm².

Methods: The cantaloupe rind surfaces were placed at a distance of 8.9 cm from the outlet of the flash unit and the effect of wet steam treatment at 65 ± 2^oC for 60 s, 120 s, and 180 s was investigated. The initial population of aerobic mesophilic bacteria, yeast and mold and lactic acid bacteria on control cantaloupe rind surfaces averaged 6.5 ± 0.22, 2.8 ± 0.12 and 3.3 ± 0.12 log CFU/cm², respectively.

Results: Steam treatment at 60s, 120s and 180s reduced the aerobic mesophilic bacteria to 4.2, 3.1 and 2.3 log CFU/cm², respectively. At 120 and 180 s, the surviving inoculated populations of E. coli bacteria and lactic acid bacteria on cantaloupe rind surfaces averaged 0.6 and 0.9 log CFU/cm², respectively, while yeast and mold populations were below detection.  E. coli bacteria plated on Violet Red Bile Agar, with 5 ml overlay of the same agar containing 4-methylumbelliferyl-beta-D-glucuronide (MUG) increased by 4 CFU only.

Significance: The results of this study suggest that wet steam treatment can be used to reduce microbial populations of cantaloupe rind surfaces and enhance microbial safety of whole and fresh cut cantaloupe pieces to reduce or eliminate illness and costly recalls due to foodborne outbreaks.