Self-Diffusion and Temperature Mapping of Food Materials Using MRI

Abstract

170 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993.Properties of water in foods play an important role in food processing. Molecular self-diffusion of water is affected by a variety of parameters, including chemical composition, internal structure, and temperature of foods. Studying self-diffusion noninvasively using magnetic resonance imaging (MRI) techniques is useful for understanding dynamic phenomena which occur during food processing. The overall objective of this study was to measure the self-diffusion coefficient using magnetic resonance imaging (MRI) techniques and convert the self-diffusion images to temperature images.A gelatin-sucrose gel system was used to study the effects of composition and temperature on the self-diffusion coefficient. Parameters studied were composition, amount of gelatin, sucrose and distilled water, and temperature. A combined-orthorgonal central composite experimental design was conducted. A nonlinear regression model, representing the self-diffusion coefficient as a function of composition and temperature, was obtained. Results showed that the self-diffusion coefficient increased significantly as temperature increased, and decreased as solids concentration increased.Temperature is an important control parameter in food processes and thermal properties determination. Two dimensional self-diffusion coefficient images of a potato cylinder were obtained using MRI during heating and converted into temperature images. The initial temperature of the potato was 20\sp\circC, and the heating water temperature was 50\sp\circC. Non-magnetic thermocouples were implanted into the potato at different depths. The MRI and thermocouple data were acquired simultaneously. The error in the MRI temperature measurements caused by noise and the time delay to acquire each data set was less than 0.84\sp\circC, and the average variation between the MRI and thermocouple temperature measurements was less than 0.5\sp\circC.Thermal properties of the potato were calculated using the MRI temperature mapping data. The thermal diffusivity of the potato was 1.36 \times 10\sp{-7} m\sp2/s and the thermal conductivity of the potato was 0.599 W/m\sp\circC. The convective heat transfer coefficient between the potato and heating water ranged from 589.36 to 119.20 W/m\sp2\sp\circC corresponding to heating times of 1 min to 4 min, respectively.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD