基于温度控制的猕猴桃片微波真空干燥特性研究

Microwave-vacuum drying characteristics of kiwifruit slice based on controlling temperature

目的:研究温度控制下猕猴桃片微波真空干燥特性,并确定其最佳数学干燥模型。方法:以猕猴桃片为原料,利用自制的温度自适应微波真空干燥机干燥猕猴桃片,研究不同控制温度、真空度和微波功率密度对其干燥特性和水分有效扩散系数的影响,利用SPSS 19.0软件将试验数据与6个常用的薄层干燥模型进行非线性拟合,以确定系数R^(2),均方根误差R_(MSE)及卡方χ^(2)作为评价指标,筛选出最佳干燥模型。结果:温度控制条件下的猕猴桃片的微波真空干燥为降速干燥过程,无明显恒速阶段。在试验范围内,控制温度与真空度对猕猴桃片的干燥特性影响显著,控制温度越高、真空度越大,物料的干燥速率越大;根据费克第二定律计算出猕猴桃于温度控制下微波真空干燥过程中的水分有效扩散系数,且随着控制温度与真空度的增大而增大,其最大值为6.81497×10^(-6) m^(2)/s,平均活化能为70.77 kJ/mol。所选用的6个模型中,Two-term exponential模型具有最大的确定系数R^(2)(0.9999),最低的R MSE(0.00202)和最小的χ^(2)(0.00030),是猕猴桃片温度控制下微波真空干燥的最佳模型。结论:控制温度、真空度对猕猴桃片微波真空干燥特性、干燥速率和水分有效扩散系数具有显著影响。在试验范围内,Two-term exponential模型的拟合度最高,可有效描述猕猴桃片温度自适应下微波真空干燥过程中的水分随时间的变化规律。

Objective:To improve the dry product quality and drying efficiency of kiwifruit slices(KS),the effects of microwave-vacuum drying conditions with controlling temperature on the drying characteristics of KS were studied and the drying kinetics model was established to predict the moisture change in the drying process.Methods:Using KS as raw materials,the effects were studied,including in different setting temperature,vacuum degree and microwave power density on the drying characteristics of KS and its effective moisture diffusion coefficient(EMDC)of water,and the activation energy was also calculated.With the R^(2),R_(MSE) andχ^(2) as the evaluation indexes,the six common dry models were screened with fitting the experimental data by SPSS 19.0 software,the relationships between the model parameters and drying conditions was established.Results:Microwave-vacuum drying process of KS occurred in the falling-rate period,and there was no constant drying rate period.Under the experiment conditions,setting temperature and microwave power density had a certain influence on the microwave-vacuum drying characteristics of KS.With the increase of setting temperature and vacuum degree,the drying rate increased.However,the effect of microwave power density was not significant.The water effective diffusion coefficient of the KS during drying process could be calculated by Fick’s second law,and it increased with the increase of setting temperature and vacuum degree.The maximum EMDC was 6.81497×10^(-6) m^(2)/s.Arrhenius was used to calculate the activation energy of KS in drying process and the value of Ea was 70.77 kJ/mol.Among the six models,the Two-term exponential model had the highest coefficient of determination R^(2)(0.9999),the lowest chi-squareχ^(2)(0.00030)and R MSE(0.00202),and it is the optimum model of the KS in microwave-vacuum drying with setting temperature.Conclusion:The setting temperature and vacuum degree had influence on the drying curves,the drying rate curve and EMDC,and the effect of microwave power density was not significant.Two-term exponential model could properly describe the microwave-vacuum drying behavior of KS,and could be used to predict the moisture change of the KS in microwave-vacuum drying process based on the temperature controlling under the test conditions.