Objective To investigate the correlation between intrinsic components, visual color, and antioxidant activity during the “nine-steaming and nine-sun-drying” processing of Heshouwu (Polygoni Multiflori Radix, PMR), providing a reference for determining the processing degree and quality control. Methods A colorimeter was used to objectively quantify the color of samples at different steaming and sun-drying cycles. HPLC was used to establish fingerprints, HPLC-Q-TOF-MS was employed to analysis characteristic peaks. Alcohol-soluble extract content was determined according to the Chinese Pharmacopoeia (2025 edition). Polysaccharide content was measured using the phenol-sulfuric acid method. Antioxidant activity was evaluated through DPPH radical scavenging capacity, ABTS radical scavenging assays, and ferric reducing antioxidant power (FRAP) method to determine total antioxidant capacity. Pearson correlation and regression analyses were conducted between the components, color values, and antioxidant activity. Cluster analysis, principal component analysis (PCA), and partial least squares regression (PLSR) were applied to determine the processing stages of “nine-steaming and nine-sun-drying” PMR, while entropy-weighted TOPSIS was used to identify its the optimal processing endpoint. Results During processing, the sample color gradually darkened, and chromaticity values decreased. Polysaccharide content increased progressively, while alcohol-soluble extract content first increased and then declined. A total of 26 chromatographic peaks were identified in the fingerprints, and the components of 25 of them were identified. Correlation analysis revealed significant relationships between intrinsic components, color values, and antioxidant activity. The processing stages were divided into initial, middle, and final phases, with the seven steaming and sun-drying cycle achieving the highest comprehensive score. Conclusion Significant changes in component content, color, and antioxidant activity occur during the processing of PMR, with notable correlations among them. The integrated “color-component-antioxidant activity” analysis enables objective discrimination of processing techniques and quality control in “nine-steaming and nine-sun-drying” PMR.

Polygoni Multiflori Radix  /  nine-steaming and nine-sun-drying  /  color-component-antioxidant activity  /  correlation analysis  /  processing  /  gallic acid  /  5-HMF  /  stilbenes glycosides  /  emodin-8-O-β-D-glucoside  /  physcion-8-O-β-D-glucoside  /  emodin  /  physcion