Product Quality and Drying Characteristics of Intermittent Heat Pump Drying of Ganoderma tsugae Murrill

Intermittent drying has been reported as an innovative drying technique for the drying of thermolabile materials in terms of energy cost and product quality. However, the effect of intermittency () on the quality of Ganoderma tsugae during intermittent drying process remains unknown. In this study, drying characteristics and product quality of continuous and intermittent drying of Ganoderma tsugae in a heat pump dryer were investigated. The color change of dried Ganoderma tsugae was compared with other drying methods such as oven drying and vacuum oven drying. Experimental results show that intermittent heat pump drying of Ganoderma tsugae reduced the effective drying time compared to continuous heat pump drying but retained lower water-soluble polysaccharides content as the intermittency decreased from 0.67 to 0.2. Nevertheless, heat pump drying of Ganoderma tsugae conducted in continuous or intermittent mode at low drying temperature produced better product quality in terms of total color change (E) and chroma value compared to oven-dried and vacuum-dried products. Lowest E and highest chroma value were obtained for =0.2, followed by =0.33 and =0.67.