Inactivation kinetics of pathogenic bacteria in persimmon using the combination of thermosonication and formic acid.

Four models (Baranyi, modified Gompertz, log-logistic and Weibull models) were applied to examine the performance of thermosonication (TS) and formic acid (FA), individually and in combination, at three temperatures (40, 50, and 60 °C) for the inactivation of pathogens inoculated on persimmon. Results indicated that all nonlinear kinetic models provided a good fit to data; however, the Baranyi showed the best performance in fitting data. The combined treatment of FA and TS had a higher negative impact on the microbial population compared to each treatment alone. The highest lethal impact was observed at 60 °C and in TS-3%FA treatment, which reduced the initial population of Escherichia coli, Salmonella enterica subsp. enterica, and Listeria monocytogenes (8.1 log CFU/mL) to 2.2, 1.6, and 1.3 log CFU/mL, respectively. Hence, the obtained models can be used to predict the inactivation of pathogens in a food model subjected to the combined treatment of thermosonication and FA.

Comparison between response surface methodology and genetic algorithm analysis to optimize lactic acid production by Lactobacillus rhamnosus and Lactobacillus acidophilus under ultrasonic pretreatment.

This work compared response surface methodology (RSM) and genetic algorithm (GA) analysis to optimize the lactic acid content by Lactobacillus rhamnosus PTCC 1637 and Lactobacillus acidophilus PTCC 1643 in a medium based on date syrup. Three parameters including concentrations of sucrose [10 and 20% (w/w)] and yeast extract [1, 2 and 3% (w/w)] along with different amplitudes of ultrasound (30 kHz, 25 and 50%) were investigated in terms of their impacts on both viable cell counts and lactic acid production. Regarding RSM and GA, optimized samples were selected by achieving high lactic acid concentration. The results indicated that an increase in the amounts of sucrose and yeast extract led to increasing the cell growth and lactic acid production. Application of ultrasound at 25% amplitude significantly (P < 0.05) stimulated the fermentation process. However, increasing the amplitude to 50% significantly (P < 0.05) decreased the lactic acid production compared with the control samples. The best treatment was observed at 20% sucrose, 3% yeast extract and 25% ultrasound amplitude. The present results indicate that the best productivity of lactic acid can be achieved at appropriate fermentation conditions, including a suitable amplitude of ultrasound and supplementation of date syrup.