Effect of particle size and concentration on foodborne pathogen inactivation by pulsed ohmic heating in tomato sauce

This research investigated the effects of the size and concentration of diced tomato particles in tomato sauce on the performance of pulsed ohmic heating (POH). Samples were prepared by adding 5 and 10 g of tomato particles (square shapes with sides of 2.5, 5, 10, and 15 mm) to 20 and 15 g of tomato sauces, and tomato sauce without particles was used as the control group. As the size and concentration of tomato particles increased, the passage of electric current was hindered, resulting in a decrease in electrical conductivity and consequently a deceleration in the heating rate of POH. Through infrared camera image analysis, it was determined that tomato particles formed cold areas in the tomato sauce, inhibiting uniform heating of POH. Because particles reduced efficiency of POH, there was an inverse relationship between the size and content of particles and the reduction of pathogens. At 20% tomato particles, the reduction levels of Escherichia coli O157:H7 were 1.60, 1.85, 2.12, 2.28, and 3.07 log CFU/ml for tomato sauces with particle sizes of 2.5, 5, 10, and 15 mm and without particles, respectively. When the size of the tomato particles was the same, increasing the particle concentration in the sauce from 20 to 40% resulted in an average reduction of 0.47 in the inactivation levels of E. coli O157:H7 by POH. Therefore, the size and concentration of particles dispersed in food should be contemplated when designing a POH process to inactivate harmful bacteria in food.