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Imaging and modeling of the microstructure of frozen foods during recrystallization and sublimation : A case study on plant-based products

Abstract : Freezing process is used for preserving food quality and extends storage life. However, food microstructure may alter due to the formation and changes of ice crystals. This may lead to structure related quality changes and loss of stability of food. 3D data on microstructure changes of frozen fruit and vegetables is currently lacking, although this may help in optimizing the freezing process. This research work applied both tomography imaging and mathematical modeling approaches for better understanding of the microstructural changes in fruit and vegetables, and important process-microstructure-quality interactions during freezing and frozen storage.A new X-ray µCT based method to characterize plant-based products was developed using Xray attenuation coefficients of reference samples. Apple tissue samples were frozen using different freezing rates: slow freezing (2.0 °C per min.), intermediate freezing (12.6 °C per min.) and fast freezing (18.5 °C per min.). Temperature-controlled X-ray µCT was optimized and utilized to image the 3D microstructure and ice crystal distribution at a voxel resolution of 3.8 µm. The three different freezing rates studied produced different ice crystal size distributions and showed a significant effect on the microstructure of the frozen apple tissue. The number of ice crystals decreased with decreasing freezing rate while the pore size distributions became narrower regardless of the different freezing rates employed. The X-ray µCT imaging technique developed was utilized to quantify the evolution of ice crystals in frozen carrots during storage. Temperature fluctuations during cold storage cause ice recrystallization that leads to microstructural and quality changes. X-ray µCT was applied to investigate 3D ice crystal changes in carrot during 2 months of storage at a dynamic change of temperature. The studied conditions revealed a significant increase in ice crystal size during the storage period. The mean equivalent diameter of the ice crystals increased, while the number of ice crystals decreased. The results presented here provide insights to describe microstructure evolution in frozen vegetables during storage for a better control of the cold chain sector.A mathematical model to describe the evolution of the ice crystal size distribution in frozen carrot tissue during dynamically changing temperatures was introduced. The model was based on a population balance equation that incorporated the ice crystal size distribution and a lumped heat transfer model. Ice recrystallization was governed first by the dissolution of small crystals and then redeposition at the surface of large crystals. This was observed mainly at the beginning of storage, and gradually decreased as storage time proceeded. The model was validated by predicting ice recrystallization using 3D ice crystal data in carrot tissue stored under dynamically changing temperature conditions, and can be useful for better management of the product microstructure in the frozen foods chain. Finally, effects of temperature fluctuations on quality changes of apple tissue during storage were assessed. To this end, apple tissue samples were frozen and subsequently stored in three different freezers set at -12 ± 3 oC, -18 ± 3 oC, and -23 ± 3 °C. In each freezer, three different compartments were created to achieve different amplitudes of temperature fluctuations: (i) low (± 0.1 °C), (ii) medium (± 0.5 °C) and (iii) large (± 1.8 °C. Frost formation, drip loss, color changes and ascorbic acid content were measured during five months of storage. The results revealed that apple quality was strongly affected by the temperature fluctuations and storage duration. The kinetic models were calibrated and validated using the experimental data. The temperature dependency was successfully incorporated using an Arrhenius equation. In addition to the kinetic model, a simplified physical model was applied to predict frost formation.
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Submitted on : Saturday, October 23, 2021 - 7:45:11 PM
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  • HAL Id : tel-03399090, version 1

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Victor Vicent. Imaging and modeling of the microstructure of frozen foods during recrystallization and sublimation : A case study on plant-based products. Chemical and Process Engineering. Institut agronomique, vétérinaire et forestier de France; Université catholique de Louvain (1970-..), 2019. English. ⟨NNT : 2019IAVF0011⟩. ⟨tel-03399090⟩

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