Modeling of transport mechanisms and quality changes during the microwave frying of foods by solving hybrid mixture theory-based unsaturated transport equations coupled with maxwell's equations of electromagnetism

Shah, Yash Dharmesh

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https://hdl.handle.net/2142/130000 Copy

Description

Title

Modeling of transport mechanisms and quality changes during the microwave frying of foods by solving hybrid mixture theory-based unsaturated transport equations coupled with maxwell's equations of electromagnetism

Author(s)

Shah, Yash Dharmesh

Issue Date

2025-05-23

Director of Research (if dissertation) or Advisor (if thesis)

Takhar, Pawan S

Doctoral Committee Chair(s)

Xu, Changmou

Committee Member(s)

• Stasiewicz, Matthew J
• Kamruzzaman, Mohammed

Department of Study

Food Science & Human Nutrition

Discipline

Food Science & Human Nutrition

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Microwaves
• Frying
• Porous matrix
• Transport phenomena
• Modeling

Abstract

Microwave frying (MF) has emerged as a promising alternative to conventional frying (CF) to produce healthier fried foods with lower oil content. However, the limited understanding of the transport mechanisms involved in MF can hinder process optimization efforts. Porous media modeling can help address this gap. In this research, the MF of foods was modeled by solving hybrid mixture theory-based two-scale unsaturated transport equations and Maxwell's equations of electromagnetism. The food matrix was modeled as a deformable and viscoelastic material. Modeling the MF of foods is challenging due to the multiple phases (gas, water, oil, and solids) and physics (heat transfer, mass transfer, deformation, and electromagnetics) involved in the process. A stepwise approach was employed wherein the model complexity was increased in each step. First, a previous CF model developed in our research group was modified and solved to account for viscoelastic deformations. Then, the microwave drying of foods was modeled as it is simpler than MF due to the absence of the oil phase. Finally, MF was modeled. Frying and microwave drying experiments were conducted to collect the model validation data. While earlier frying models in the literature ignored the volume changes of foods during frying, the CF model developed in this research accounted for the deformation of the food matrix by utilizing the pore pressure (p_pore) as the driving force governing deformation. The negative gauge p_pore near the sample surface during frying was expected to have caused the contraction of the surface layers, and the potato sample shrank by 18.5% for a frying time of 300 s. The p_pore is also expected to impact the oil penetration in foods during frying. The oil content of the sample increased significantly in the first minute of frying when the p_pore in the food was low. The oil content profile plateaued in the intermediate frying stages. This was expected due to an increase in the magnitude of p_pore in the sample. The p_pore attained a peak value of 19.2 kPa (gauge) at the sample center. The subsequent decrease in p_pore was expected to have enabled the oil uptake by the sample in the later frying stages. During microwave drying, the electric field was centrally concentrated in the cylindrical potato sample. However, the heat concentration behavior was size-dependent. The high magnitudes of pressure in the sample core (peak gauge p_pore at the center: 103.8 kPa) during microwave drying caused outward moisture movement and an expansion of the core. The magnitude of microwave power dissipation decreased in the drier parts of the sample, which may help avoid internal burning and aid the 'moisture-leveling' effect of microwave drying. Sensitivity analysis revealed a significant impact of changes in microwave frequency on the drying of foods. Experiments showed that MF at 2.45 GHz frequency led to the highest heating rates and pressure magnitudes (peak values at the sample center: 107.3°C and 24.9 kPa), followed by MF at 5.8 GHz frequency (peak values: 104.1°C and 20.8 kPa) and CF (peak values: 100.5°C and 13.8 kPa). Below a moisture content value of 3 g/g solids, the oil content of French fries increased rapidly with a decrease in moisture content for CF and relatively slowly for MF. The stress relaxation data of French fries indicated that MF at 5.8 GHz can produce crunchier fries, potentially due to intense crust heating at this frequency. Simulations with the MF model showed that MF produced samples with lower oil content than CF at a given endpoint moisture content (3-33% reduction in oil content). MF also reduced frying times by 33-76%. The spatiotemporal distribution profiles for variables like electric field, microwave power dissipation, temperature, pressure, and moisture content were analyzed. The power dissipation followed the drying front in the French fries during MF. This can cause the thickening of the crust and make the French fries crunchier. MF at 2.45 GHz led to samples with lower oil content than MF at 5.8 GHz, likely due to the deeper penetration of microwaves and higher magnitudes of p_pore in the sample during the former. Processing implications were discussed, and suggestions were made for future improvements to the design of the microwave fryer prototype used in this research. The results from this work improved the understanding of the transport mechanisms involved in MF.

Graduation Semester

2025-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/130000

Copyright and License Information

Copyright 2025 Yash Shah

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