US scientists have carried out a study on cantaloupe, honeydew and watermelon. Fruits were purchased from a local supermarket (Winter Haven, FL), stored at 4°C, and brought to 23°C prior to start the experiment. The whole fruits were disinfected by immersion in a solution of 200 ppm chlorine, then they were minimally processed and cut into 10±1 g cubed pieces (flesh only).
Afterwards, cubes were inoculated with a four-strain cocktail of L. monocytogenes, resulting in ca. 103 CFU/10g sample; the samples were stored at 4, 10, 15, 10 and 25 ±2 °C, and the enumeration of pathogens was performed at specific time intervals
The pathogen growth rate increased as the storage temperature increased.
The scientists have used the square root model to describe the L. monocytogenes growth rate as a function of temperature. The model has been compared to other prior mathematical models used both for Salmonella and Escherichia coli O157:H7 detection and for the predictive microbiology on L. monocytogenes kinetics (ComBase).
The square root model developed in this study predicts:
1. A faster growth of L. monocytogenes compared to Salmonella and E. coli O157:H7 at temperature below 20°C;
2. An increase of 4 log CFU after 15 days of storage at 5°C, and of 1 log CFU after 6 days of storage at 4°C.
The developed model resulted accurate in predicting L. monocytogenes growth in cut melons, and it may be a fast and cost-effective alternative to lab methods to estimate the effects of storage temperature on the pathogen kinetics.
