Objective To elucidate the dynamic changes in moisture, color, and index components during the “sweating” process of Danshen (Salviae Miltiorrhizae Radix et Rhizoma, SMRR) and preliminarily explore the correlation between moisture migration, color evolution, and changes in index components. Methods SMRR samples from Shandong underwent the “sweating” process, low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) were employed to analyze moisture migration and distribution characteristics. The high-performance liquid chromatography (HPLC) and colorimeter were used to determine the contents of salvianolic acid B, tanshinone II_A, tanshinone I, cryptotanshinone and chromaticity values (L^*,a^*, b^*, and ΔE) of SMRR at different “sweating” degrees, respectively, followed by Pearson correlation analysis. Results The “sweating” process mainly involved free water loss, with relaxation peak gradually shifting leftward. MRI results indicated that moisture migrated from the core to the exterior of the roots. The cross-sectional color transitioned from the outer to inner layers, changing from yellowish-white to brown and finally to purplish-brown, with the L^* decreasing while a^*, b^*, and ΔE increasing continuously. The contents of salvianolic acid B and tanshinones initially increased and then decreased, reaching the highest values in lightly sweated SMRR (SD3, 47.38 mg/g) and moderately sweated SMRR (SD7, 4.62 mg/g) respectively. The content of salvianolic acid B exhibited a significant correlation with L^*, a^*, b^* and ΔE (P < 0.01). Conclusion By clarifying the characteristics of moisture migration and distribution during the “sweating” process of SMRR, this study scientifically validates the traditional view that “sweating promotes the outward diffusion of internal moisture in medicinal materials”. It reveals the dynamic changes in color and index components during “sweating” and preliminarily explores the role of moisture in driving the color deepening from the outside to the inside and changes in salvianolic acid B content, providing a reference for optimizing the “sweating” process of SMRR.

Salviae Miltiorrhizae Radix et Rhizoma  /  sweating  /  moisture migration  /  color change  /  dynamic characteristics  /  magnetic resonance imaging  /  salvianolic acid B  /  tanshinone II_A  /  tanshinone I  /  cryptotanshinone