Analysis of Equilibrium moisture content and L-ascorbic acid during hot air drying for sweet potato

摘要

The drying characteristics and L-ascorbic acid changes of sweet potato samples were investigated during hot air drying at four temperatures ranging from 30 to 60 deg C. Equilibrium moisture contents (EMC) of sweet potato samples in the desorption process were measured at various temperatures by a static method. The measured results were fitted to the Chen-Clayton equation. Using both the measured moisture content data in the drying test and the EMC values, the drying process was evaluated with a combination of both the exponential drying model and an infinite plane sheet model for the diffusion equation. The diffusion coefficient was calculated using an infinite plane sheet model. An Arrhenius-type equation was used to estimate the diffusion coefficient of sweet potato in response to temperature, and the activation energy of sweet potato during hot air drying was estimated. In order to examine the nutrient changes in sweet potato during hot air drying, a first-order reaction rate equation was applied to changes in the decomposition of L-ascorbic acid contents during hot air drying. An Arrhenius-type equation was also applied to estimate the decomposition rate coefficient k'. Accordingly, the activation energy needed for decomposition during hot air drying of sweet potato was estimated to be 48.8 kJ- mor~(-1).