Multidimensional Quality Evaluation of Drying Methods on the Bioactive Components and Antioxidant Activity of Astragalus membranaceus var. mongholicus Slices

This study systematically evaluated the effects of five drying methods (sun drying, freeze drying, shade drying, and hot air drying at 40 °C and 60 °C) on the multidimensional quality of Astragalus membranaceus var. mongholicus slices using multiscale techniques and multivariate analysis. The results showed that the drying methods significantly influenced color, microstructure, volatile organic compound profiles, the content of 13 bioactive constituents, and antioxidant activity. Among all treatments, hot air drying at 40 °C achieved the highest composite score in the comprehensive evaluation. This treatment was associated with a marked increase in surface microroughness (Ra), higher levels of the pharmacopoeial markers astragaloside IV and calycosin-7-O-β-D-glucoside, and enhanced ABTS radical scavenging activity. However, other methods performed better in individual parameters: shade drying showed higher DPPH and FRAP values, while freeze drying gave the highest total phenolic content. Based on the observed strong correlations (e.g., roughness vs. astragaloside IV: r = 0.94; astragaloside IV vs. ABTS: r = 0.83), we propose a testable hypothesis that hot air drying at 40 °C may influence bioactivity partly through physical microstructural changes. The multidimensional evaluation framework established here provides a methodological reference for quality optimization of medicinal and edible herbs.