Modeling Heat Transfer In Cantaloupes During Hot Water Immersion And Thermal Destruction Of Listeria monocytogenes

Open Access
Ramachandran, Radhika
Graduate Program:
Food Science
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 15, 2013
Committee Members:
  • Ramaswamy C Anantheswaran, Thesis Advisor
  • Cantaloupe
  • Listeria monocytogenes
  • modeling
  • hot water immersion
The Listeria monocytogenes outbreak in 2011, associated with the consumption of cantaloupes was responsible for numerous cases of listeriosis and 33 deaths. There is a need to develop a suitable postharvest treatment to ensure that cantaloupes are free of Listeria monocytogenes. The overall goal of this research was to determine the effect of a thermal treatment process, in the form of hot water immersion, to enhance the microbiological safety of cantaloupes. The specific objectives of this research were: (a) to study the potential of microbial penetration into whole cantaloupes by conducting dye penetration and surface inoculation of L. monocytogenes on whole cantaloupes, (b) to develop a finite element model to simulate the time-temperature distribution within cantaloupes during heating and to validate the finite element model by conducting hot water immersion studies on cantaloupes, and (c) to determine the destruction of L. monocytogenes on surface inoculated cantaloupes by subjecting them to hot water immersion. In the dye penetration study, whole cantaloupes were immersed in dye solution to study the maximum distance of penetration into cantaloupes. In the surface inoculation study, whole cantaloupes were inoculated with a cocktail of L. monocytogenes strains L2624, L2625, L2626, and L2676, the strains that were associated with the 2011 cantaloupe outbreaks. The cantaloupes were inoculated on the surface with this cocktail in order to determine the extent of microbial penetration into the fruit. A finite element model of cantaloupes was used to determine the time-temperature distribution in them, when heated by immersing in hot water at different temperatures, and this model was validated using hot water immersion experiments with cantaloupes. Based on the results from the finite element model, the inoculated cantaloupes were subjected to hot water immersion on day 0 of inoculation at temperatures of 850C and 950C for 5 minutes. The dye penetration study showed that the maximum penetration was up to 1 cm inside the fruit. During the surface inoculation study with cantaloupes, the maximum cell population was recorded on day 0 of inoculation and the maximum cell penetration was up to 1 cm into the cantaloupes. The predicted time of heating from the finite element model for hot water immersion at 850C and 950C was 5 minutes in order for the temperature at positions 5 mm beneath the surface to reach 750C and 850C, respectively. The hot water immersion of inoculated cantaloupes at 850C and 950C for 5 minutes showed that the thermal treatment reduced L. monocytogenes by 3.46 ± 0.31 log10 CFU/ml and 4.88 ± 0.18 log10 CFU/ml, respectively. Populations of L. monocytogenes recovered from cantaloupes that were subjected to hot water immersion at 850C and 950C for 5 minutes were significantly lower than those of the controls (P < 0.05). The results presented in this research show that hot water immersion treatments have the ability to reduce levels of Listeria monocytogenes in cantaloupes contaminated with this pathogen. Additionally, the simulation model of heat transfer indicated that while the temperature of the rind elevated rapidly, the pulp of cantaloupes remained at room temperature. This feature of hot water immersion treatment is an advantage if such a treatment is considered as a post harvest treatment process because it does not increase the temperature of the pulp, thereby not affecting the sensory properties of the cantaloupe.