辣椒热泵干燥特性及工艺参数优化

Heat pump drying properties of chili and optimization of technical parameters

为了提高干制辣椒品质,降低干燥能耗,该文应用热泵干燥技术干燥辣椒。首先探究干燥温度和铺料厚度对干燥特性的影响,绘制出含水率和干燥速率变化曲线。在此基础上,将分阶段控温和改变铺料厚度结合起来对辣椒进行热泵干燥,运用响应面法中的Box-Behnken设计,考察第一阶段温度、第二阶段温度、铺料厚度和三者的交互作用对品质得分、单位能耗、干燥时间的影响,并建立回归方程,得出最佳工艺参数。结论如下:温度越高,干燥速率越大,含水率下降越快;铺料厚度越大,干燥速率越小,含水率下降越慢;第一阶段温度是影响单位能耗的主要因素(P<0.05),较低的第一阶段温度能降低单位能耗;第二阶段温度对品质得分影响显著(P<0.05),对干燥时间影响极显著(P<0.01),第二阶段温度在60℃左右时能得到品质较佳的干辣椒,且在一定程度上提高了干燥效率;铺料厚度对品质得分、干燥时间的影响极显著(P<0.01),对单位能耗的影响显著(P<0.05),铺料厚度在45 mm左右干燥获得的辣椒品质较佳,而且能节约能耗,提高干燥效率。综合优化参数为:第一阶段温度48℃、第二阶段温度61℃、铺料厚度44 mm,在此工艺条件下获得的干燥辣椒品质得分为8.64,单位能耗为92.05 k J/kg,干燥时间为896.02 min。研究结果为热泵干燥技术应用于辣椒干制提供参考。

Chili is a kind of spicy vegetable in the genus Capsicum member of the nightshade family, with the essential condiment components of polyphenols, carotenoids, capsaicinoids, vitamin C and E and other nutrients. Although it is easy for fresh chili into mildew condition, dried chili can not only be preserved for a long time, but also increase economic benefits. However, the ordinary drying method for chili, especially sun-drying is restricted by natural conditions, and chili is easy to be polluted by pests, microorganisms, and dust. Among different techniques of drying worldwide, heat pump drying technology is commonly used in chili drying and it has the advantages of improving the quality, saving energy and improving efficiency in the process of drying. In this paper, we designed a fruit and vegetable drying integrated machine for the experiments at College of Engineering, Nanjing Agricultural University with Xuzhou Haitao Refrigeration Company. The effects of the first stage temperature, the second stage temperature, the material thickness and the interaction of these 3 factors on comprehensive score, unit energy consumption and drying time were investigated. These parameters were optimized through the response surface method with 3 factors as well as 3 levels. Linear weighting method was used to analyze comprehensive multi-objective optimization, and regression equations of 3 indices were developed based on the experimental data. The experimental results revealed that the effect of temperature on the drying rate is important, a higher temperature means a higher drying rate, and in the temperature range of 55-65 ~C, there is a significant increment in drying rate. Similarly, the material thickness also has a great impact on the drying rate. If the material is thicker, then the drying rate is lower; and if the thickness is more than 50 mm, it results in the obvious decrease of drying rate. The first stage temperature, the second stage temperature, and material thickness have significant impacts on comprehensive score, unit energy consumption and drying time. The major factor affecting unit energy consumption was the first stage temperature （P〈0.05）. Lower first stage temperature could reduce unit energy consumption. The major factor affecting comprehensive score and drying time was the second stage temperature （P〈0.05）. Lower second stage temperature was beneficial to the quality of dry chili and reduced time consumption during the drying. The quality of dry chili is excellent when the second stage temperature is about 60 ℃. The material thickness had an obvious influence on the comprehensive score, unit energy consumption and drying time （P〈0.01）. The quality of chili was better when the material thickness was about 45 mm. When the first stage temperature, the second stage temperature, and material thickness were 48 ℃, 61 ℃ and 44 mm, respectively, the Composite quality score was 8.64, the unit energy consumption was 92.05 kJ/kg and the drying time was 896.02 min. These were the optimal results got from the 3 evaluation indices. The research provides a theoretical basis for the application of heat pump drying technology in chili drying.