Modeling water loss during frying of potato slices

The effect of blanching and drying on water loss and oil uptake during potato slice frying was studied. Two pretreatments were carried out for the slices: (i) blanching in hot water at 85 degrees C for 3.5 min; (ii) blanching in hot water at 85 degrees C for 3.5 min and then, air-dried until a moisture content of 60% (wet basis) was obtained. A control treatment, consisting of unblanched potato slices not air-dried was also conducted. After the pretreatments, potato slices were deep-fried in sunflower oil at 120, 150, and 180 degrees C. With respect to the control treatment, blanching provided an increase while blanching-drying a decrease of the oil uptake. Two models, based on Fick's law, were used to describe water loss during frying. The first one is the classic model with an effective moisture diffusion coefficient, which assumed a constant value. The second model considers that the diffusion coefficient varies during the frying process. The variable diffusivity model adjusted the experimental data much better than the constant diffusivity model did. The effective moisture diffusion coefficient, in the variable diffusivity model, increased with frying time and temperature and behaved very similar for both control and blanched slices, while the increase of this coefficient was considerable higher for the blanched-dried slices. The development of a more porous structure with less oil content in the case of blanched-dried slices could explain this fact.