莲子微波真空干燥特性及其微观结构的分形特征

Microwave Vacuum Drying Characteristics of Lotus Seeds and the Fractal Characteristics of Their Microstructures

本文研究了不同干燥参数(微波强度和真空度)对莲子微波真空干燥特性、微观结构和宏观物性(收缩率和复水率)的影响,利用盒计数法定量描述微波真空干燥莲子微观结构的分形特征,并以标准分形维数(ΔFD/FD0)来构建微波真空干燥莲子宏观物性(收缩率和复水率)与微观结构间的函数关系。结果表明,莲子干燥至平衡含水量所需时间随微波强度或真空度的增加而减小。莲子收缩率随微波强度的增加呈现先减小后增加的趋势,而复水率则呈现出先增加后减少的趋势;随真空度的增加,莲子收缩率逐渐减小,而复水率呈现出先增加后减少的趋势。分析维度可定性描述微波真空干燥莲子的微观结构,分形维数越大,莲子的复水率和收缩率就越大,同时分形维数与复水率和收缩率间具有良好的线性关系,可用分析维度来推测莲子的物理特性。

Lotus seeds are dried for storage.The effects of microwave vacuum drying（MVD） on lotus seeds were assessed.The effects of different drying parameters（microwave power density and degree of vacuum） on the drying characteristics,microstructure,and physical properties（shrinkage and rehydration） of lotus seeds were studied.A box counting method（BCM） was used to quantitatively describe the fractal characteristics of the microstructure of dried lotus seeds.The normalized change of the fractal dimension（ΔFD/FD0） was used to construct the functional relationship between physical properties,including shrinkage and rehydration,and the microstructure of lotus seeds dried by MVD.The results indicated that the time required for lotus seeds to be dried to equilibrium moisture content decreased with increasing microwave power density or degree of vacuum.With increasing microwave power density,the shrinkage of lotus seeds initially decreased but subsequently increased.Additionally,the rehydration of lotus seeds initially increased but subsequently decreased.The shrinkage of lotus seeds decreased gradually with an increase in the degree of vacuum（from-60 k Pa to-90 k Pa）.However,the rehydration of lotus seeds initially increased and subsequently decreased.The analysis of dimension could qualitatively describe the microstructure of the lotus seeds dried by MVD.Shrinkage and rehydration of lotus seeds increased with an increase in ΔFD/FD0.The higher the fractal dimension,the higher the degrees of lotus seed shrinkage and rehydration.Furthermore,a linear relationship was observed between ΔFD/FD0 and shrinkage/rehydration,and the fractal dimension analysis could be used to predict the physical properties of lotus seeds.