(191a) Hybrid Mixture Theory-Based Modeling of Moisture Transport in Carrots during Drying

It is necessary to understand the water transport phenomenon occurring in a food product since it plays an important role by affecting its functional properties during processes. It influences the appearance, structure, texture, and ultimately consumer acceptance of a product. Proposed models in the literature have primarily used Fickian type diffusion to describe the water transport in biopolymers. These models fail to include the effect of glass transition and relaxation of the structure during adsorption/desorption on water transport and swelling. Therefore, in this study, the moisture transport mechanism during drying process was elucidated for carrots using numerical solution of hybrid mixture theory (HMT) based multi-scale fluid transport equations, which include the stress relaxation terms. The drying experiments were performed in an environmental chamber (Associated Environmental Systems, Ayer, MA, USA) controlling the temperature and the relative humidity of the environment for drying of carrots up to 4 hours. The stress relaxation data, required for the transport equations, was obtained using a dynamic mechanical analyzer (DMA). The three-element Maxwell model was fitted well to describe the viscoelastic behavior of carrots (R²>0.999, RMSE <2.08x10^-4). Since drying causes shrinkage throughout the sample, the transport equations were transformed from the Eulerian coordinates to the stationary Lagrangian coordinates. Numerical simulations gave data on temporal and spatial profiles for moisture, viscoelastic stress distribution, and shrinkage. Good agreements between the experimental and the predicted values of moisture content and volume changes were obtained. During simulations, the center of the carrots was observed as the region with the highest moisture content while the boundaries presented the lowest values. Also, the HMT based non-Fickian transport model was coupled with kinetic equations representing the quality attributes of carrots, such as color and texture to predict these attributes as a function of drying time. The results of the color parameters (L, a, and b), showing decreasing trends between 30.12-51.58% after 4 h drying, were compared with the model predictions. In overall, the created model provided significant information to fundamentally describe the underlying mechanisms that occur during the drying process. The simulations showed that the moisture transfer, the shrinkage effect, and the quality attributes can be predicted with reasonable accuracy. This model would allow determining the optimum drying conditions to obtain improved product quality and prolongation of the shelf-life for food products like carrots.