Multiscale modeling of transport mechanisms, strain, and stress in food products subjected to drying

Abedi, Fidele Massindi

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https://hdl.handle.net/2142/120210 Copy

Description

Title

Multiscale modeling of transport mechanisms, strain, and stress in food products subjected to drying

Author(s)

Abedi, Fidele Massindi

Issue Date

2023-03-17

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

Takhar, Pawan S

Doctoral Committee Chair(s)

Lee, Youngsoo

Committee Member(s)

• Rausch, Kent D
• Wang, Yi-Cheng

Department of Study

Food Science & Human Nutrition

Discipline

Food Science & Human Nutrition

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Drying
• Stress
• Strain
• Stress-cracking
• Multiscale modeling
• Hybrid Mixture Theory
• Rice
• Banana
• ripening
• stress relaxation

Abstract

The strain and stress that develop in food materials during drying play a critical role in the formation of stress cracks, material failure, and other associated quality parameters such as shape, microbial quality, and processability. Specifically, stress cracks can form in food materials during drying due to a variety of factors, including an excessive stress gradient between adjacent layers or when some layers undergo glass transition in the presence of a high stress gradient. Therefore, a fundamental understanding of the development of strain and stress and its relation to the mechanisms of moisture transport is crucial for controlling the formation of stress cracks and the failure of food materials. This understanding cannot be obtained through purely experimental approaches alone. The Hybrid Mixture Theory (HMT)-based modeling equations were solved to describe the development of strain and stress in plantain bananas and rough rice as representative food materials. The food materials were treated as two-scale, two-phase, linear viscoelastic bodies composed of a mixture of solid and water phases. The velocity of the water phase with respect to the solid phase was described by the generalized Fick’s law of Takhar, which couples viscoelastic relaxation with fluid flow. As a result, the modeling equations accounted for Fickian transport in the glassy and the rubbery states, where the timescales of moisture diffusion are significantly lower and higher than the timescale of viscoelastic relaxation, and non-Fickian transport near the glass transition region, where the timescales of diffusion and viscoelastic relaxation are of the same order of magnitude. In the case of the banana’s model, the multiscale moisture transport equation was also coupled with a multiscale heat transport equation. The deformation associated with drying was incorporated by transforming the transport equations from Eulerian to Lagrangian coordinates, and the computation was done using finite element-based commercial software. The variables predicted by the modeling equations were moisture content, strain, viscoelastic stress, temperature, and energy consumption for the banana and moisture, strain, and viscoelastic stress for rice. The models were used to evaluate the susceptibility of stress crack formation by analyzing the stress gradient along the axial direction (banana) and the small minor axis (rice), as well as the glass transition phenomena that affect some layers of the materials.The stress relaxation properties of ripe plantain bananas were measured in temperature and moisture content ranges of 40-80 C and 0.17-1.84 g/g solids, respectively, to describe their viscoelastic behavior during drying. The two-element generalized Maxwell model was fitted to data collected experimentally through nonlinear regression, and coefficients G0, G1, G2, and relaxation times 1, and 2 were obtained. At all temperatures, as moisture content decreased, the stress relaxation coefficients also decreased, indicating a softening of the banana.The modeling equations were validated by conducting drying experiments and comparing the predicted results with experimental values. The validation focused on the average moisture content (MAEs: 0.022-0.121 g/g solids), temperatures (MAEs: 0.8-8.1 C), and volumetric strain (MAEs: 0.06-0.13) for the banana. For rice, the validation was done for the average moisture contents for two varieties of rice, an India variety and a US variety (MAEs: 0.0079-0.0162 g/g solids and 0.0022-0.0061 g/g solids, respectively). Simulations studies investigated the susceptibility of stress crack formation when bananas and rice are dried under continuous conditions compared to when intermittent and time-varying drying conditions are used. Results from simulating the drying of bananas showed that drying them at 60 C by turning the fan on and off intermittently would reduce stress crack formation compared to continuous drying, with only a slight increase of 0.9 % in energy supplied. Conclusions drawn from the simulation results were confirmed experimentally by measuring the cracks formed in bananas using a global crack index on a 5-point hedonic scale. Simulation results for rice showed that a time-varying drying strategy where the inlet air temperature is gradually increased by 5 C steps every 5 minutes after an initial period of constant temperature drying at 40 C for 28.5 minutes would dry rice entirely in the glassy state. It would also result in a moderate stress gradient along the semi-minor axis and lower stress crack formation.The modeling equations can be used in research and development to design and optimize drying parameters and reduce stress crack formation in rice, banana, and banana-based products. They can also be used routinely as part of a quality monitoring scheme.

Graduation Semester

2023-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Fidele Abedi

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