Multiscale modeling of transport mechanisms and quality changes in frozen foods during freeze-thaw cycles

The freezing process is commonly used to store and preserve foods. However, the frozen foods’ texture and taste are harmed by the temperature fluctuations during shipping and storage. The insights into the mechanisms of heat transfer, moisture migration, ice crystallization and solute diffusion are necessary to be achieved to understand the complex freezing process. The objective of this study is to develop a fundamental mathematical model complemented by the experimental measurements for describing heat, fluid, species and mechanical changes in foods subjected to freeze-thaw cycles. From the experimental aspect, the 3D microstructure of frozen potatoes was investigated by using an innovative high-resolution internal imaging method: X-ray micro-computed tomography (CT), to study the effect of temperature fluctuations on ice crystal growth/decay during freezing. The inner structure and porous morphology showed significant growth of ice crystals with the increase in temperature fluctuations and duration of freezing. Besides, the 3D ice crystal morphology, size distribution and pore volume fraction obtained by image analysis provide useful information for a frozen biomaterial, which is difficult to be gathered from traditional experiments. A hybrid mixture theory-based multiscale model was applied to predict phase change, fluid, species and heat transfer, crystal growth, and thermomechanical effects inside the frozen products during freezing. A solution scheme for the two-scale unsaturated transport and thermomechanical equations was developed, which can explain the fluids, species and heat transfer and describe the physical mechanisms during the freezing process. Good agreements between the predicted values and experimental data were achieved with regard to temperature profiles and freezing point depression (FPD). This work is the first study to calculate FPD in a porous food using HMT based fluid and species transport model. The simulation results show that HMT-based solute transport equation coupled with fluid and heat transfer equations and physical chemistry-based relations can provide a better prediction of the freezing point depression than the empirical equation published in the literature. Furthermore, this solution scheme is capable of identifying the freezing efficiency of air and liquid-based freezing media. The predicted results for a frozen potato in the air blast freezer indicated less ice formation and more mass loss compared to the sample in the ethylene glycol-based freezer. The practical application of this study is the analysis of the effect of temperature fluctuations on certain quality attributes of frozen foods. Larger magnitude and longer duration of fluctuations for the ambient freezing temperature increase the gas volume fraction and result in its uneven distribution from center to surface, which indicates that the pores are enlarged and cell walls are prone to be damaged in the frozen biomaterial. In addition, the frozen potato geometry presented varying deformation for the fluctuating conditions. The sudden temperature fluctuation situations representing opening and closing of freezer door were also investigated using this solution scheme. The predicted results manifested that multiple door opening-closing conditions would show worse damage to the frozen product quality in comparison to the one with fewer fluctuations.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Agricultural & Biological Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2020

Author dc:creator

• Zhao, Ying

Contributors dc:contributor

• Takhar, Pawan
• Feng, Hao
• Wang, Xinlei
• Padua, Graciela

• Multiscale modeling, freezing process

Statement dc:rights

• Copyright 2019 Ying Zhao

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/106376

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/106376