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MATHEMATICAL MODELING AND MICROBIOLOGICAL VERIFICATION OF OHMIC HEATING OF SOLID-LIQUID MIXURES IN CONTINUOUS FLOW OHMIC HEATER SYSTEMS

Kamonpatana, Pitiya
http://rave.ohiolink.edu/etdc/view?acc_num=osu1343490087

Abstract Details

2012, Doctor of Philosophy, Ohio State University, Food, Agricultural and Biological Engineering.
Currently, the world’s food industry has great interest in producing high-quality shelf-stable foods, in particular liquid foods containing solid pieces. One of the promising technologies for this purpose is continuous ohmic heating, which involves the passage of an alternating electrical current for the purpose of internal heat generation. To ensure sterility in continuous ohmic heating systems, the slowest-heating solid piece needs to receive sufficient heat treatment at the outlet of the post-heating holding section. Because in-situ noninvasive temperature measurement of moving pieces in continuous flow is not feasible, this research aims to develop mathematical models, coupled with microbiological validation, to ensure that the entire product is rendered sterile. For this purpose, it was necessary to study a sufficiently large number of samples to ensure that at least one scenario involving a fast-moving particle in the 99th percentile was sampled. A residence time distribution (RTD) study was conducted in a pilot-scale ohmic system using radio frequency identification (RFID) methodology to determine the residence time of a sample of at least 300 particles. The mathematical model, consisting of solution of the electric field, flow, heat transfer and inactivation kinetic problems, coupled with the information from the RTD study, computed the lethal effect of the cold spot of such a solid particle, and predicted the required size of the holding tube. Thermal verification of the mathematical model was conducted to compare the simulated temperatures with experimental temperature profiles for the liquid phase at the outlet of heating and holding sections. Finally, microbiological validation of the model was conducted using at least 300 solid pieces, each individually inoculated with Clostridium sporogenes ATCC 7955 (PA 3679) spores, which were processed through the system, recovered and cultured to determine if survivors existed post-processing. It was also necessary to conduct such trials at two different temperature conditions, one corresponding to a sufficient thermal process, and the other, to an underprocessing scenario. Two projects were successfully conducted: 1) sliced water chestnut in starch solution in a continuous flow heater with flow perpendicular to the electric field and 2) chicken chow mein product (viscous sauce with chicken pieces, cut celery, cut mushroom, bean sprouts and sliced water chestnut) in a continuous flow heater with flow parallel to electric field. The residence time of the fastest-moving particle was 0.75 times the product mean residence time in the heating section and 0.90 in holding tubes for the first project; and 0.64 and 0.84 for the second project. Based on the residence times, the model predicted a requirement of 15.85 m tube length at 134.0C process temperature with 1.6x10-4 m3/s volumetric flow rate to achieve target lethality at the cold spot of the slowest-heating particle for the first project; and 22.00 m for 139.6C with 1.0x10-4 m3/s for the second one. Thermal verification showed good agreement between calculation and experimental fluid temperature (P>0.05) for both cases. In addition, with the predicted length of the holding tubes, microbiological validation tests with at least 300 samples indicated the absence of viable microorganisms at the target treatment and positive growth below target, thereby verifying the model predictions. Heating rates of solid-liquid mixtures in continuous ohmic heating depend on their electrical conductivities. The most desirable situation is when the conductivities of two phases are comparable, since the uniformity in heating can be achieved. Pretreatment protocols were conducted to increase and decrease the conductivity of solid particles. A blanching method in higher and lower conductivity media was developed to increase and decrease the electrical conductivity of celery. However, blanching alone was insufficient to alter the electrical conductivity of chicken and mushroom. Marination of chicken and combinations of vacuum infusion and blanching for mushroom in appropriate media for the appropriate lengths of time could raise the electrical conductivity. The measurement of the electrical conductivity of chicken/alginate particles with different formulations was also investigated. The data obtained could aid in selecting the chicken/alginate particles having electrical conductivity lower than two standard deviations below the slowest-heating particle as a representative of the slowest-heating particle used in the microbiological validation. Further, this information may be used as a guide for food processors to adjust electrical conductivities of food solid components for a solid-liquid mixture processed in ohmic heating systems. In conclusion, it was evident that continuous ohmic sterilization processes can produce safe solid-liquid foods. The experiment demonstrated the ability of the mathematical model to ensure food safety and gain insight into the process.
Sudhir K. Sastry, PhD (Advisor)
Ahmed E. Yousef, PhD (Committee Member)
Gonul Kaletunc, PhD (Committee Member)
165 p.
Agricultural Engineering; Food Science; Microbiology
Mathematical modeling; simulation; ohmic heating; continuous ohmic heating; continuous flow ohmic heater system; solid-liquid mixture; microbiological verification; microbiological validation; residence time distribution;

Recommended Citations

Citations

  • Kamonpatana, P. (2012). MATHEMATICAL MODELING AND MICROBIOLOGICAL VERIFICATION OF OHMIC HEATING OF SOLID-LIQUID MIXURES IN CONTINUOUS FLOW OHMIC HEATER SYSTEMS [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343490087

    APA Style (7th edition)

  • Kamonpatana, Pitiya. MATHEMATICAL MODELING AND MICROBIOLOGICAL VERIFICATION OF OHMIC HEATING OF SOLID-LIQUID MIXURES IN CONTINUOUS FLOW OHMIC HEATER SYSTEMS. 2012. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1343490087.

    MLA Style (8th edition)

  • Kamonpatana, Pitiya. "MATHEMATICAL MODELING AND MICROBIOLOGICAL VERIFICATION OF OHMIC HEATING OF SOLID-LIQUID MIXURES IN CONTINUOUS FLOW OHMIC HEATER SYSTEMS." Doctoral dissertation, Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343490087

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.
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