Effect of glutinous components on matrix microstructure during the drying process of plant porous materials

Abstract

Abstract This paper compares the drying of two plant materials by microwave drying and hot air drying using Chinese angelica and Astragalus slices as examples, with the aim to study the influence of glutinous components in plant tissue on drying behavior of plant materials. In cases studied in this paper, the microwave drying time of Chinese angelica slices is reduced to 1/16 (50 min/810 min), that of Astragalus slices is reduced to 1/6 (30 min/180 min) as compared to hot air drying. The total pore volume of hot air dried Chinese angelica slices sample is 1.5 times of microwave dried sample, but that of microwave dried Astragalus slices sample is 2.5 times of hot air dried sample. In compare to microwave dried sample, the re-hydration ratio of hot air dried sample of Chinese angelica slices sample increases by 7.1%, but that of Astragalus slices sample decreases by 6.6%. This can be partly explained by the characteristics of pore size distribution inside matrix, resulted by the less deformation of glutinous component inside matrix during microwave drying process as compared to hot air drying. It is also confirmed that larger porosity and total volume of sample, higher re-hydration ratio of sample.