Abstract: Heat pump drying device was used for the drying of whole litchi. The drying curves and dry curve rates of litchi in steady condition were determined. The conversion rate of water content during combinatorial drying processing of heat pump and microwave drying was analyzed. The effects of heat pump drying temperature, the conversion rate of water content, and microwave drying time on the quality of litchi during combinatorial drying processing were investigated. Orthogonal test results indicated that the order of drying efficiency on the quality of litchi were heat pump drying temperature, conversion rate of water content and microwave drying time. The optimal drying parameters were heat pump drying temperature of 50 ℃, conversion rate of water content of 100% and microwave drying time of 2.5 min. Under the optimal processing conditions, the score of comprehensive sensory evaluation was 27.

Key words: heat pump, microwave, combinatorial drying, litchi