Absrtact: In order to improve the drying efficiency and quality of fresh apple slices, the moisture transfer and thermal image characteristics of apple slices in three drying processes, i.e. microwave hot air fluidized bed drying, microwave vacuum drying and electrothermal blast drying, were studied by low field nuclear magnetic resonance analysis and imaging (NMR/MRI). The color of dehydrated apple slices under different drying conditions was studied by color difference meter. Texture and microporous structure.
The results show that with the continuous drying process, the peak value of main signal A2i shifts to the left, and the main state of water gradually becomes difficult to flow and bound water. Among them, the total signal A2 decreases rapidly in the first half of the drying cycle of hot air drying process, which indicates that the crust on the surface of materials hinders the water transfer and the drying of water becomes more difficult; the temperature field of microwave hot air fluidized bed drying becomes more difficult. The uniformity of microwave vacuum drying is higher than that of microwave vacuum drying, which indicates that hot air and fluidized bed have positive effects on improving the uniformity of microwave drying.
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