Microwave Vacuum Drying Characteristics of Lotus Seeds and the Fractal Characteristics of Their Microstructures
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Abstract:
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 kPa to -90 kPa). 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.
