Effect of drying techniques on extraction of Astragalus pieces

To investigate the effect of different drying techniques on the quality of Chinese herb medicine (CHM), drying experiments of Astragalus pieces after rehydration were carried out, and four different kinds of drying techniques viz microwave drying, freeze-drying, vacuum drying and hot-air drying, were examined in this paper. The microstructure of dried samples was characterized by means of scanning electron microscope (SEM), and the molecular weight distribution of Astragalus pieces extract was characterized by means of ultrafiltration. Results show that dehydrated rate by microwave drying is five times faster than those by others three drying techniques. The effective component content in the extract of sample dried by microwave drying, with the molecular weight of less than 4000 Da, is higher than those by other three drying techniques. Observations of the SEM images show that the microstructure of sample dried by microwave drying is much similar to that of raw Astragalus pieces, indicating that microwave technique helps keep the penetrability of inner transmission tissues and thin-wall cell tissues, and benefits to the extraction of effective components of Astragalus pieces. (C) 2010 Curtin University of Technology and John Wiley & Sons, Ltd.