Abstract: This study aimed to improve the quality parameters of heat pump dried long cowpea such as rehydration characteristics and color, and simultaneously to lower energy consumption during heat pump drying and increase drying efficiency. The rehydration ratio, color difference, per-unit energy consumption and drying time were investigated with respect to three independent variables, namely drying temperature, blanching time and material density. A multiple regression model was developed for each of these response variables in order to optimize the selected independent variables. A blanching time of 3 min, a material density of 2 kg/m2 and a drying temperature of 50 ℃ were determined as the optimal conditions. Under these conditions, the experimental values of rehydration ratio, color difference, per-unit energy consumption and drying time were 1.15, 22.39, 14.31 (kW·h)/kg and 7 h, respectively, which were very close to the predicted ones. These optimized process conditions can provide a useful basis for heat pump drying of cowpea.

Key words: heat pump, drying, cowpea, Box-Behnken design, optimization