Optimization of a variable-temperature heat pump drying process of shiitake mushrooms using response surface methodology

Quality, energy consumption, and production efficiency are paramount factors for optimizing a shiitake mushroom drying process, which are often mutually restrained. This paper adopts the response surface methodology to optimize a variable-temperature drying process of shiitake mushrooms based on a comprehensive score considering the above three aspects. A mode-switchable heat pump drying system is specially built to implement a variable-temperature drying process including four stages in which drying temperatures are 35 °C, 45 °C, 55 °C, and 65 °C, respectively. It is demonstrated that the drying time at 55 °C is the most important factor affecting the rehydration ratio of dried shiitake mushrooms, and the drying time at 35 °C is the key factor affecting the coefficient of performance of the heat pump. Moreover, according to the comprehensive score, the optimal drying time at 35 °C, 45 °C, 55 °C, and 65 °C are 2.4 h, 3.3 h, 5.6 h, and 2.6 h, respectively. The comprehensive score of the optimal drying process is 0.837 which is 49% higher than that of constant-temperature drying at 65 °C. One striking fact is that a valuable theoretical and experimental guideline is provided for future research on heat pump drying of shiitake mushrooms.