香椿芽热泵式冷风干燥模型及干燥品质

为获得干燥速率快、品质高的香椿芽制品，以新鲜香椿芽为原料对其进行冷风干燥处理，研究不同干燥条件下香椿芽的干燥特性；采用Weibull函数模型对干燥曲线进行拟合并分析干燥过程；以干燥时间、干燥能耗、叶绿素含量、VC含量以及复水率为指标对不同条件下香椿芽冷风干燥过程进行加权综合评价；以热风干燥和真空冷冻干燥为参照，对比研究较优冷风干燥参数下香椿芽干制品的品质。结果表明，提升干燥温度、进口风速以及减少装载厚度均能显著减少香椿芽冷风干燥耗时（P＜0.05），不同干燥条件对干燥耗时的影响程度由大到小为：温度＞进口风速＞装载厚度；Weibull函数模型能够准确描述香椿芽冷风干燥过程中水分含量变化过程（R2＞0.9），其形状参数均小于1，整个干燥过程为降速干燥，主要由内部水分扩散控制；香椿芽冷风干燥有效水分扩散系数在（6.272～9.637）×10－9 m2/s之间，均属于10－9数量级，且受温度的影响最大；当干燥温度、装载厚度和进口风速分别为20 ℃、3.0 mm、2 m/s时，香椿芽冷风干燥的综合评分值最高，实验范围内，该条件较适合应用于香椿芽的冷风干燥中；相对于热风干燥而言，冷风干燥产品的品质更接近真空冷冻干燥产品的品质。

Drying Modelling and Quality of Toona sinensis Subjected to Heat Pump Cold Air Drying

In order to obtain high drying rates and high-quality dried products, a heat pump dryer with cold air was applied to dry fresh Toona sinensis, and the drying characteristics under different drying conditions were investigated. The drying data were fitted to the Weibull distribution function and the drying process was analyzed by investigating the parameters of the Weibull distribution function. The weighted comprehensive evaluation of Toona sinensis under different drying conditions was carried out based on drying time, energy consumption, chlorophyll content, VC content and rehydration ratio. The quality of cold air dried products obtained under the optimum drying conditions was evaluated by comparing with hot air drying and freeze drying. Results showed that increased drying temperature and inlet velocity and reduced loading thickness significantly (P < 0.05) reduced the cold air drying time of Toona sinensis, and the effect of different drying conditions on drying time was in the decreasing order of temperature > inlet velocity > loading thickness. The Weibull distribution function could accurately describe the change in water content of Toona sinensis during cold air drying (R2 > 0.9) with a shape parameter less than 1. The whole drying process was falling-rate drying, and was mainly controlled by internal moisture diffusion. The effective moisture diffusivity of Toona sinensis was in the range of (6.272–9.637) × 10－9 m2/s, and it was influenced most significantly by drying temperature. The highest comprehensive score of cold air dried Toona sinensis was obtained under the conditions: drying temperature of 20 ℃, loading thickness of 3.0 mm and inlet velocity of 2 m/s. Compared with hot air drying, the quality of cold air dried products was closer to that of vacuum freeze dried products.