Astragalus membranaceus: Impact of postharvest drying processes on yield and components of bioactive compounds

Abstract

Drying of the roots is a typical postharvest process in the production of the widely used Traditional Chinese Medicinal herb Astragalus membranaceus but there is limited understanding of its effect on quality. This study investigated drying and steaming treatments to address how quality is affected by postharvest processing. It was found that the total content of bioactive components in A. membranaceus decreased by 46 % when dried at 40 °C; 78 %−82 % when dried at 40 °C, then steamed and dried again at 40 °C, 60 °C or 80 °C; and 67 % when steamed and dried at 40 °C. Steaming prior to drying resulted in a chemical profile less different from drying alone or double drying when compared with fresh, having the highest level of calycosin-7-O-β-D-glucoside and lower levels of its metabolites. Drying and double drying resulted in deglycosylation of calycosin-7-O-β-D-glucoside into calycosin and formononetin. Despite significant decrease in bioactive content, the least altered composition of samples steamed prior to drying may indicate inactivation of enzymes and present an alternative postharvest process depending on the desired chemical profile of the A. membranaceus product.