Studies on the Microstructure and Quality of Iron Yam Slices during Combined Freeze Drying and Microwave Vacuum Drying: Microstructure of Iron Yam during FD-MVD
Studies on the Microstructure and Quality of Iron Yam Slices during Combined Freeze Drying and Microwave Vacuum Drying: Microstructure of Iron Yam during FD-MVD
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DOI：
10.1111/jfpp.12459
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发表时间：
2015-04
影响因子：
2.5
通讯作者：
Huang Luelue;F. Qiao;C. Fang
中科院分区：
文献类型：
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作者：
Huang Luelue;F. Qiao;C. Fang
冷冻干燥（FD）4.5h-微波真空干燥（MVD）的铁山药片在容重、色泽等方面与FD样品基本相同，在以前的实验中。本文通过对试样微观结构的比较，验证了这一点。此外，还对不同转变点的试样进行了显微组织和质量测试，以阐明其晶胞结构的变化机理以及显微组织与相应质量之间的关系。水分转化点和熔点对试样的微观结构有显著影响。通过FD3.5 h-MVD干燥的样品与熔融样品的细胞结构保持得非常好。而在FD 2 h-MVD标本中观察到明显的细胞壁断裂甚至塌陷。质量指标如体积密度和颜色与显微结构变化呈正相关。FD3.5 h-MVD与FD4.5 h-MVD相比，其质量几乎相同，但干燥时间更短。在以往的研究中，冷冻干燥（FD）-微波真空干燥（MVD）的最佳水分转化点通常是升华阶段的结束。此时，样品中没有明显的冰晶，这表明材料均匀地吸收微波能量，导致最终产品的质量高。然而，对于富含淀粉的蔬菜和水果材料，例如铁山药，预先选择水分转换点。冷冻干燥后，样品中的冰晶在低温下缓慢融化，水分重新分布均匀。由于原料淀粉颗粒的支持，材料的结构保持得很好。因此，在此工艺条件下也可获得高质量的干品。总体而言，FD-MVD干燥的能耗进一步降低，同时物料的质量保持良好。
The quality of freeze drying (FD)4.5 h-microwave vacuum drying (MVD) iron yam slices was almost the same with FD samples in terms of bulk density, color, etc., in the previous experiments. This work verified it by comparing the microstructure of the samples. In addition, the microstructure and quality of samples with different conversion point during combined FD and MVD were tested in order to illuminate the change mechanism for cell structure and the relationship between microstructure and corresponding quality. Moisture conversion point and melting significantly affected the microstructure of samples. The cell structure of samples dried by FD3.5 h-MVD with melting samples was maintained very well. However, obvious cell wall breakage and even collapse was observed in FD2 h-MVD samples. Quality indices such as bulk density and color are positively related to microstructure change. FD3.5 h-MVD with melting was better than FD4.5 h-MVD because of almost the same quality and shorter drying time. Practical Applications In most previous researches, the optimal moisture conversion point was usually the end of sublimation stage during freeze drying (FD)-microwave vacuum drying (MVD). There was no obvious ice crystal in sample at this point, which showed that the materials absorbed the microwave energy uniformly and caused high quality of final products. However, for vegetables and fruits materials that are rich in starch, such as iron yam, moisture conversion point was chosen in advance. Ice crystal in the samples melted slowly in low temperature and well-distributed moisture again after FD. The structure of the materials was maintained very well because of the support from raw starch granules. Therefore, high-quality dried products were also obtained under this technique conditions. In general, energy consumption for FD-MVD drying was decreased further while the quality of the materials was maintained well.