Numerical modeling of heating tomato pulp in continuous flow microwave-assisted thermal processing: Estimation of quality parameters

Continuous thermal treatment of tomato pulp aims for microbial and enzyme inactivation with minimal quality degradation. The objective of this work was to model the thermal treatment of tomato pulp flowing continuously inside a microwave cavity and a holding tube. The three-dimensional model considers the Navier-Stokes, thermal energy conservation, Fourier's law of heat conduction, and Maxwell's equations of electromagnetism. The tomato pulp was pseudoplastic, and the phase change during heating was considered using an equivalent specific heat capacity. The model calculated the effect of diameter of the applicator tube (D-t), volumetric flow rate (v?$$ \dot{v} $$), and processing temperature (T over bar out$$ {\overline{T}}_{out} $$) on Bacillus coagulans inactivation, lycopene and color degradation, and furan formation for a thermal treatment sufficient to reduce six logarithmic cycles of the spoilage microorganism. The results revealed that tomato pulp flowing in a tube with 38 mm diameter absorbed 98% of the electromagnetic power input. However, in terms of the food nutritional and sensory quality attributes, the better design parameter was the microwave system operating with a 42 mm diameter tube. Furthermore, the tomato pulp quality also was improved when the processing temperature increased from 100 degrees C to 120 degrees C (reduction of 77% of furan, and reduction of 88% and 90% of lycopene and color degradation, respectively), and in this process condition, the effect of the tube diameter on the quality attributes ceased to be important. Practical applications This work presented a numerical simulation-based study to enhance the microwave-assisted thermal processing design for liquid foods. The mathematical tool developed here allows a detailed evaluation of the electromagnetic power dissipation and temperature profiles in the tomato pulp and how these parameters affect microbial inactivation and the food's nutritional and sensory quality attributes. These results contribute to understanding the microwave heating system and guide microwave equipment manufacturers. Furthermore, the model can be useful for optimizing and controlling microwave-assisted pasteurization/sterilization processes.