Fundamental Understanding of Cellular Water Transport Process in Bio-Food Material during Drying

Abstract

Bio-food materials are heterogeneous in structure with cellular diversity, where the majority of the water is located in the intracellular spaces. Understanding of the nature of the microscopic behaviour of water transport is crucial to enhance the energy efficiency in food processing and obtain the better quality of processed food. In this research, apoplastic and symplastic transport of cellular water in the bio-food material during drying was investigated using 1H-NMR-T2 relaxometry. We found that intracellular water (ICW) migrates from intracellular spaces to the intercellular spaces by progressive rupturing the cell membranes while drying at a higher temperatures (60 °C–70 °C). In this case, apoplastic process dominates the transport process. However, at lower temperature (45 °C), cell membranes do not rupture and therefore ICW migrates from cell to the neighbouring cell through micro-capillaries, where the symplastic process dominates the mass transfer at different stages of drying.

A multiscale approach to estimate the cellular diffusivity during food drying

“…Additionally, different cellular deformation can occur when drying at different temperatures (Khan, Farrell, Nagy, & Karim, 2018;Mahiuddin, Khan, Kumar, Rahman, & Karim, 2018).…”

“…For convective drying, the drying air temperature generally dictates what cellular deformation occurs. For example, when convective drying at temperatures below 50 C, cells generally remain intact and the composition of cellular water (water within different cellular environments) remains fairly consistent throughout the entire drying period (Khan, Farrell, et al, 2018). When convective drying at temperatures above 50 C, cell rupturing occurs, drastically changing the amount of water within different cellular environments (Khan, Farrell, et al, 2018), causing all three stages of cellular deformation to occur.…”

“…For example, when convective drying at temperatures below 50 C, cells generally remain intact and the composition of cellular water (water within different cellular environments) remains fairly consistent throughout the entire drying period (Khan, Farrell, et al, 2018). When convective drying at temperatures above 50 C, cell rupturing occurs, drastically changing the amount of water within different cellular environments (Khan, Farrell, et al, 2018), causing all three stages of cellular deformation to occur. Khan, Farrell, et al (2018) investigated this phenomenon with NMR and X-ray tomography demonstrating when cells collapse, water rushes out of the cells, moving from the intracellular spaces to intercellular spaces and thus becomes free water (FW)].…”

“…When convective drying at temperatures above 50 C, cell rupturing occurs, drastically changing the amount of water within different cellular environments (Khan, Farrell, et al, 2018), causing all three stages of cellular deformation to occur. Khan, Farrell, et al (2018) investigated this phenomenon with NMR and X-ray tomography demonstrating when cells collapse, water rushes out of the cells, moving from the intracellular spaces to intercellular spaces and thus becomes free water (FW)]. This is visually represented in Figure 1 (c).…”

“…This requires minimal microstructural knowledge but forces the effective diffusivity to be isotropic. These microscale domain approximations are constructed from ICW/FW ratios published in Khan, Farrell, et al (2018) which were measured using NMR, details outlined in section 2.2.6. Anisotropic diffusivity is outside the scope of the current work, however, it can be introduced into this model but ungrouping the intercellular spaces, considering the real cellular structure of the material or considering an off-centered circle.…”