Effects of multiphase microwave drying on the microstructure of Chinese yam: A study based on X-ray micro-computed tomography technology

To address the issues of long drying time and high equipment costs present in freeze drying and freeze drying-microwave vacuum combined drying techniques, as well as to obtain higher-quality dried products, multiphase microwave drying (MMD) has been proposed. This study investigated the effects of MMD at different transition point moisture content levels (0.36, 0.59, and 0.79 g/g d.b.) on the microstructure and texture of dried Chinese yam. Using freeze drying (FD), microwave freeze drying (MFD), and microwave vacuum drying (MVD) as controls, X-ray micro-computed tomography (micro-CT) visualized and quantified Chinese yam's structure across drying methods. The results indicated that as the transition point moisture content increased, the porosity and connected pore area and volume decreased, while non-connected pore area and volume increased. Chinese yam samples obtained from MMD scheme I (transition point moisture content of 0.36 g/g d.b.) exhibited a uniform and porous structure with a high total porosity (48.19 ± 0.32%), similar in hardness and shrinkage to freeze-dried yams, preserving microstructural integrity. MMD reduced drying time and maintained the quality of dried Chinese yam compared to FD, MVD, and MFD, highlighting its potential as a cost-effective method for producing premium dried Chinese yam products.