Kinetics of forced convective air drying of potato and squash slabs / Cinética del secado de rodajas de patatas y calabacin con corriente de aire

Moisture content, temperature, and surface area variations of potato and squash slabs were measured during forced convective air drying; the effect of the initial moisture content on drying behaviour was also investigated. A mathematical model that numerically integrated the diffusion equation and the thermal balance for a three-dimensional shrinking slab was used to simulate the drying process. The parameters of the model (surface area, heat transfer coefficient and dry solid density) were experimentally determined. Fitting parameters (activation energy and pre- exponential coefficient in the Arrhenius equation) were found by comparing experimental and predicted drying curves. Good agreement was obtained down to a moisture level of 0.4 kg water/kg dry solid. Diffusion coefficients were independent of their moisture content within the range studied for both products. The activation energies for potato and squash were 2.09 x 104 kJ/kg mol and 3.76 x 10 4 kJ/kg mol, respectively. Changes in the rates of drying and heating curves for potato took place at moisture levels around 0.4 kg water/kg dry solid, but this was not the case for squash. The differences were mainly attributed to the different shapes of the sorp tion isotherms.

Modeling moisture migration in a multi-domain food system: Application to storage of a sandwich system

Moisture transport in a food system involving two different materials of unequal moisture content was modeled with water activity as the driving force using a porous media framework. This model was applied to a bread-barbecue chicken pocket sandwich stored in isothermal conditions. The model successfully predicted the equilibrium condition, where the two materials, bread and chicken, reached the same water activity, but not the same water content. The transient changes in the moisture content in the bread and chicken were predicted and shown to be significantly affected by air gap between the bread and chicken. The prediction process was also sensitive to the Darcy permeability values for the materials. The modeling framework presented for a sandwich system is very general and can easily be extended to other multicomponent food systems.

Microstructural changes of osmotically dehydrated tissues of apple, banana, and potato

Scanning electron microscopy examination was conducted on osmotically dehydrated tissues of apple, banana, and potato. High-quality stereo images and surface parameters were recorded from two sets of samples: fresh samples and osmotically dehydrated samples for each material studied. Scanning electron microscopy micrographs revealed that osmotic treatment had a significant effect on the structural properties (cell wall, middle lamella) for the different plant materials. The intercellular spaces were larger for materials treated at higher temperature (55 degrees C) and higher concentration of sucrose solution (70%). The cell wall and middle lamella observed in Golden Delicious apple appeared larger than those in Cox apple, banana, and potato, and probably contributed to the observed descending order of water loss and solid gain as: Golden Delicious > Cox > potato > banana.