Drying characteristics of Shiitake mushroom and Jinda chili during vacuum heat pump drying

Drying characteristics of the Shiitake mushroom and Jinda chili, a commonly grown variety in the Northeast of Thailand, was investigated under varying conditions of the drying temperatures (50, 55, 60 and 65 °C) and the vacuum pressures (0.1, 0.2, 0.3 and 0.4 bar) in a new design of a vacuum heat pump dryer. Nine different thin layer mathematical drying models were compared according to their correlation coefficient, reduced chi-square and root mean square error to estimate vacuum heat pump drying curves. The result indicates that the Midilli model can present better predictions than the others. The constants and coefficients of this model could be explained by the effect of the drying temperature and the drying pressure. The drying temperature and pressure significantly affects color degradation (probability P < 0.05). Drying temperature has little effects on rehydration capacity (probability P > 0.05). Rehydration capacity notably decreases with an increase in the vacuum pressure.