Optimization of drying process for Lentinus edodes by combing heat pump with vacuum

Objective  To reduce the cost of processing, and obtain high quality dried Lentinus edodes.

Method  On the basis of single-factor experiment, Box-Behnken Design (BBD) was used to study the effects of heat pump temperature(A), vacuum degree(B) and conversion point moisture content(C) on unit energy consumption, sense judgment, rehydration ratio and hardness. We deduced a multinomial regression model, optimized the combined drying technology and compared with single heat pump drying and single vacuum drying.

Result  The optimal parameters were obtained as follows: The heat pump temperature was 49 ℃, the vacuum degree was 110 Pa, and the conversion point moisture content was 56%. Under these conditions, the tested unit energy consumption was 345.01 kJ·g^–1, the sense judgment was 8.3, the rehydration ratio was 2.72, and the hardness was 3.61 N, which were close to the predicted values. The relative errors were 0.19%, 3.61%, 1.47% and 1.66% respectively. The unit energy consumption of combined drying was 37.69% less than that of vacuum drying and higher than that of heat pump drying. The sense judgment and rehydration ratio of combined drying were close to those of single vacuum drying and higher than those of heat pump drying. The hardness was slightly larger than that of vacuum drying and less than that of heat pump drying.

Conclusion  The method combining heat pump drying and vacuum drying obtained dried L. edodes with low energy consumption and good quality. It solves the poor quality in heat pump drying and high energy consumption in vacuum drying. This study can provide a theoretical basis for heat pump-vacuum combined drying of L. edodes.