Characterization of heat and mass transfer during deep-fat friying and its effects on cassava chip quality

Heat and mass transfer in thin slices of fresh cassava (Manihot esculenta Crantz) were studied. The frying process was described as two stages involving inner vaporization of mainly high available water, which can be transported inside the material, at temperature around the boiling point and inner vaporization of "bound" water at higher temperature depending on water desorption equilibrium. During the first stage, drying rate was controlled by the serial association of both diffusive and convective thermal resistances. During the second stage, temperature gradients decreased and the core temperature followed the corresponding boiling curve (water desorption curve against boiling temperature). Oil uptake depended on the thermal history of the product, characterized by its final water content. Apparent elasticity modulus and color changes were similar for a same final water content. Boiling curves and core temperature measurement are therefore proposed as a means of predicting the development of chip quality during frying. (Résumé d'auteur