Modeling the growth rates of Escherichia coli spp. and Salmonella Typhimurium LT2 in baby spinach leaves under slow cooling

After field harvest, baby spinaches are transported to the packing shed where they are cooled by forced air systems. If contaminated, the temperature of spinaches will affect the number of pathogens in the leaves, and effective temperature control is critical to restrict their growth. Hence, the need to assess the impact of cooling practices on the growth of pathogens in leafy greens. The Baranyi model was used to describe the experimental data and build a dynamic model to predict microorganism growth rate in baby spinach leaves as function of temperature. Baby spinach leaves, inoculated with 10(4) CFU/ml of Salmonella Typhimurium LT2 or 10(2) CFU/ml of an Escherichia coli cocktail, and were maintained at temperatures ranging from 10 to 37 degrees C for 30 h. At 10 -30 degrees C, the E. coli strains grew significantly more (similar to 2-4 log cycles) than the Salmonella strain (similar to 0.11 -2.4 log cycles) while at 37 degrees C, both bacterial populations increased by similar to 6 log cycles for 30 h. The growth kinetics of each microorganism followed the Baranyi model. The maximum bacterial population increased with temperature and the values were similar for both bacteria. The theoretical minimum temperature for growth was 5.88 degrees C and 4.76 degrees C for Salmonella and E. coli, respectively. The dynamic model was validated with an experimental linear cooling profile (slow cooling) and could be incorporated into a risk assessment tool to evaluate the growth of pathogens in baby spinach during processing and distribution. (C) 2012 Elsevier Ltd. All rights reserved.