Hot air drying characteristics of fruits and vegetables and surface hardening of samples during drying

Drying characteristics and surface hardening of sweet potato, radish and eggplant during hot-air drying were investigated. As a result, the drying of sweet potato showed a first falling rate period, and that of radish and eggplant was composed of a constant rate period and a first falling rate period. A constant kappa c, was newly defined as the drying constant in the constant rate period. An Arrhenius type equation was used to relate the constant kappa c to temperature, which showed a good fit to the experimental data. The internal porosity of the sample increased because shrinkage of the sample was restrained by surface hardening of these samples, causing decreased density. The structural properties of samples in the drying process influenced the surface hardening of these samples.