Effects of far-infrared radiation on the freeze-drying of sweet potato

An experimental dryer was developed to determine the drying characteristics of sweet potato during freeze-drying with far-infrared radiation. The experimental drying time of sweet potato cubes dehydrated by three drying methods, i.e., air-drying, freeze-drying, and freeze-drying with far-infrared radiation, were compared, and freeze-drying with far-infrared radiation was found to be able to reduce the drying time of sweet potato. Both constant and falling rate drying periods were observed, and empirical equations were developed to study the behavior of drying rate in falling rate period. On the other hand, four mathematical models were used to describe the drying characteristics of sweet potato during freeze-drying with far-infrared radiation. The coefficients of determination (R2) in the exponential, Page, and approximate diffusion model were found to be above 0.98, and that of diffusion model was above 0.92. The rank of fitness of those models was Page, approximate diffusion, exponential and diffusion model. The choice of Page model was evident because of the lowest residual as well as RMSE. The Page model described the far-infrared freeze-drying characteristics of sweet potato properly.