Effect of microwave irradiation on chemical profile of extracts during the extraction of organic compounds from Astragalus slices

Abstract

The objective of this paper was to study the relationship between the chemical profile of extracts and the extraction behavior of plant porous materials using Astragalus water extraction as an example. The results will assist in the determination of optimal processing conditions and maintaining or improving the quality of natural products. Conventional reflux extraction (RE) and microwave-assisted extraction (MAE) were considered and compared. The molecular cutoff of ultrafiltration membranes was used to analyze the molecular weight distribution of extracts. Result shows that the yield of extracts by MAE (10 min) is significantly higher than that by RE (120 min), especially for those extracts with relative small molecular weight. Conventional hot air drying and microwave drying were also compared for further discussion on the effect of microwave irradiation on extracts. Atomic force micrograph (AFM) shows that the size of extracts (as particle height) are approximately 3.850–4.364, 6–10, and 100–300 nm for MAE-hot air drying, RE-microwave drying, and RE-hot air drying, respectively. Therefore, the results presented confirm that microwave irradiation can be used to prepare samples with uniform small size. This provides a better understanding of mass transfer behavior inside matrix during the extraction of plant materials. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.