Microwave drying characteristics and dried quality of pumpkin

Little detailed information is available on microwave drying characteristics of pumpkin and alternative microwave power drying of food products. This study focuses on describing microwave drying characteristics of pumpkin and discussing the effect of alternative drying input load-power (power at each unit initial mass), sample thickness and mass on the dried quality. Experiments were conducted to study microwave drying characteristics and dried quality, and a two-stage microwave drying using the first- and second-stage power. It has two falling rate periods using microwave drying on pumpkin: the first falling rate period at moisture content of pumpkin more than 1.6 dry basic (d.b.), and the second falling rate period at moisture content less than 1.6 d.b. The same water loss will consume more energy at moisture content less than 1.6 d.b. Dehydration rate increased and energy consumption decreased with increase of input power, decrease of mass. The thicker sample dried more rapidly than the thinner one during the first falling rate period, but during the second falling rate period, dehydration rate of the thin sample is slightly higher than that of the thick sample. The quadratic orthogonal regression experiment was conducted, and models for effect of first-stage drying load-power, second-stage drying load-power, slice thickness and first-stage drying time (four factors) on sensory quality, rehydration ratio and energy consumption rate (three indices) were established. The effect of four single-factors on three indices is significant. All the interaction effects of four factors on sensory quality and energy consumption rate are not significant. The quadratic polynomial of first-stage drying load-power on three indices is significant. Drying factor optimising combination for three indices was obtained. For three indices, drying factor-optimising combination is different. First-stage drying load-power should be higher for energy consumption rate and lower for rehydration ratio. Second-stage drying load-power should be higher for rehydration ratio, and slightly lower for energy consumption rate. Pumpkin slice thickness should be thick for three indices and can also be thin for energy consumption rate. First-stage drying time should be longer for three indices and can also be shorter for sensory quality. For three indices, the first-stage power differs from the second-stage power. This implies that the alternative microwave power drying on pumpkin should be applied.