29E-6 |
Moisture transfer in potato, apple and carrot (core and cortex) during convective hot air and microwave-convective hot air drying |
J. SRIKIATDEN and J. S. Roberts. Food Science & Technology, Cornell Univ., New York State Agricultural Experiment Station, 630 W. North St., Geneva, NY 14456-1371 Drying of food products is mainly used for preservation purpose by removing water to a level at which microbial spoilage and chemical reactions are minimized. Also with fruits and vegetables having a high initial moisture content, drying of these products is an energy intensive process. Therefore, understanding internal moisture transfer mechanisms are important to optimize the dry product and the drying process. The objective of this work is to investigate moisture transfer during drying of fruit (apple) and vegetables (potato, carrot core and carrot cortex) and the applicability of the Fickian model to predict dehydration of these materials. Convective air drying experiments of 0.7 and 1.4 cm diameter cylindrical samples were performed at 40, 50, 60, and 70oC and at air velocities of 1.5 and 3 m/s. Weight loss of the samples was measured on-line using an analytical balance interfaced to a computer. The effective moisture diffusivity was determined experimentally from the drying curves at different temperatures. Temperature profiles were measured along the radial axis. A remote infrared temperature sensor was used to measure sample surface temperature during drying. Effective moisture diffusion coefficients of 0.7 cm diameter cylindrical samples at different temperatures were 4.68x10-10-1.02x10-9 (potato), 6.42x10-10-1.48x10-9 (carrot core), 6.80x10-10-1.21x10-9 (carrot cortex) and 1.01x10-9-2.06x10-9 (apple) m2/s. Sample size and air velocity had only a significant effect on the effective moisture diffusivity of apple. Temperature dependence of the effective moisture diffusivity was found to follow the Arrhenius relationship. However, temperature profiles during convective hot air drying showed existence of temperature gradients. This explains the difference between experimental data and model predictions. Therefore, isothermal drying using an apparatus that combines microwave energy and convective hot air will be used to quantify the drying kinetics. This work provides a better understanding of the mechanism(s) that control the drying process for fruits and vegetables.
Session 29E, Food Engineering: Transport processes and kinetics
|