Numerical modeling of thermal inactivation parameters of Escherichia coli O157:H7 in pretreated watermelon juice

Aim: This work focused on numerical modeling of thermal inactivation parameters of Escherichia coli O157:H7 in pretreated watermelon fruit juice as influenced by processing conditions. The work aimed to enhance microbiological safety and information of the product. Methods: Mature and fresh watermelon fruits were sourced, graded, and processed into juice under hygienic conditions. The extracted juice was pasteurized and allowed to cool. Prior to thermal treatments, the juice was sterilized, cooled, and inoculated with Escherichia coli O157:H7. The inoculated samples were then subjected to different treatments. The effect of pH (4.5, 5.5, and 6.5) and temperature (70℃, 80℃, and 90℃) on thermobacteriological properties was investigated. Meanwhile, Design Expert 13 for Windows was used for experimental layout for interactive impact of pH and inactivation temperatures. All experiments were conducted in triplicate. Thermal inactivation curves of Escherichia coli O157:H7 in the juice samples were obtained by plotting the number of survivors (CFU/mL) against time, and the corresponding D-value was obtained. Other thermobacteriology parameters were subsequently calculated using appropriate equations. The data obtained were fitted into a model using Design Expert 13 for Windows. Results: Thermal inactivation data obtained showed that the thermal inactivation curve of Escherichia coli O157:H7 in pretreated watermelon juice had a linear interactive effect as temperature and pH varied. As temperature (70–90°C) and pH (4.5–6.5) varied, thermobacteriology parameters such as D-value, F-value, z-value and activation energy ranged from 11.8–23.4 min, 23.6–46.8 min, 8–9.6°C, 32.49–42.03 kJ/mol, respectively. The results showed that Escherichia coli O157:H7 in pretreated watermelon juice demonstrated significant inactivation at a higher temperature of 90℃ and a lower pH of 4.5. Conclusions: This study provided valuable data that could be employed as a guide for the potential food industry, scientists, and engineers in order to improve the consumption safety of the product.