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Studies on the Microstructure and Quality of Iron Yam Slices during Combined Freeze Drying and Microwave Vacuum Drying
Author(s) -
Huang Luelue,
Qiao Fang,
Fang Changfa
Publication year - 2015
Publication title -
journal of food processing and preservation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.511
H-Index - 48
eISSN - 1745-4549
pISSN - 0145-8892
DOI - 10.1111/jfpp.12459
Subject(s) - microstructure , materials science , ice crystals , moisture , microwave , sublimation (psychology) , freeze drying , melting point , breakage , mineralogy , water content , composite material , chemistry , optics , chromatography , geology , physics , psychology , quantum mechanics , psychotherapist , geotechnical engineering
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 FD 3.5 h‐ MVD with melting samples was maintained very well. However, obvious cell wall breakage and even collapse was observed in FD 2 h‐ MVD samples. Quality indices such as bulk density and color are positively related to microstructure change. FD 3.5 h‐ MVD with melting was better than FD 4.5 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.