紫花苜蓿茎秆和叶片的解吸等温线模型及参数优化

为掌握苜蓿(Medicago sativa)收获干燥过程中的解吸等温线,控制干燥过程和贮藏稳定性。文章采用镜面冷凝露点法研究了20℃,30℃,40℃条件下苜蓿顶部茎秆、中部茎秆、根部茎秆以及叶片的解吸等温线。依据5种常用等温线模型对试验数据进行了拟合,并对各拟合模型的适用性进行了分析评价,在此基础上对模型的表达式及参数进行了优化和修正,以确定最佳拟合模型及其参数。结果表明:苜蓿叶片属于Ⅱ型解吸等温线,苜蓿顶部茎秆、中部茎秆、根部茎秆都属于Ⅲ型等温线。在同一水活度条件下,苜蓿茎秆和叶片的储藏温度不同对安全含水率的要求也不同,且它们的安全含水率存在较大差异,环境温度越低对应的安全含水率越高。在20℃,30℃和40℃条件下,苜蓿叶片采用修正GAB模型拟合效果最好,顶部茎秆的最佳解吸等温线方程为GAB和Henderson模型,中部茎秆和根部茎秆适用于GAB和Oswin模型。

Water Desorption Isotherm Models and Parameters Optimization of Alfalfa(Medicago sativa) Stems and Leaves

In order to achieve the basic data for alfalfa drying process and storage stability,desorption isotherm characteristics of alfalfa stems and leaves were determined using mirror condensation dew point method at different temperatures (20,30,and 40℃,respectively).Five common models were used to fit the experimental data in non-linear regression analysis.The fitness of the models and their parameters were evaluated using Fitting Goodness and residual distribution.Based on these expressions,parameters of the models were optimized and modified to achieve the best-fit model and its parameters.The results indicated that the leaves desorption isotherm belonged to type Ⅱ,but the adsorption isotherm of stems was type Ⅲ.Under the same conditions of water activity,safe moisture contents were significantly different between alfalfa stems and leaves.The requirements of safe moisture content were also different in different storage temperatures.Under the same moisture content condition,the lower ambient temperature corresponded to the safe storage.The modified GAB were the best fitting desorption isotherm models for alfalfa leaves,and the best model fitted for the desorption isotherm of top stem was GAB and Henderson model.The GAB and Oswin were found to be the most suitable models for describing the lower stems under three temperatures (20,30 and 40℃).