Abstract: This study systematically elucidated the effect and underlying mechanism of nine cycles of steaming and sun-drying on the metabolome and antioxidant activity of Polygonatum cyrtonema rhizome. We measured changes in the mass loss rate, color, content, molecular mass and monosaccharide composition of polysaccharides, and in vitro antioxidant indices of P. cyrtonema rhizome during the process, and also carried out non-targeted metabolomic analysis. The results showed that after processing, the color significantly deepened, and the mass loss rate stabilized at approximately 67%. The molecular mass of polysaccharides significantly decreased with increasing number of processing cycles, and their distribution became more uniform. The maximum in vitro 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity, total antioxidant capacity, and hydroxyl radical scavenging capacity reached 87.67%, 25.76 U/mL, and 60.15%, respectively, and the antioxidant activity increased overall. Metabolomic analysis identified 34 significantly differential metabolites. Among these, the contents of oligosaccharides (e.g., maltotriose and stachyose) and amino acids (e.g., arginine and tryptophan) decreased, while those of DL-α-tocopherol and pyroglutamic acid increased. Correlation analysis indicated that the enhanced antioxidant activity was closely associated with substrate consumption and the generation of active products resulting from the Maillard reaction. This study revealed the material basis for the enhanced antioxidant activity of P. cyrtonema rhizome after nine cycles of steaming and sun-drying from the perspective of metabolite-activity correlation, providing a theoretical basis for standardizing the processing technology of P. cyrtonema rhizome and developing functional foods based on this material.

Key words: Polygonatum cyrtonema; nine cycles of steaming and sun-drying; metabolomics; antioxidant activity; polysaccharide; Maillard reaction