Elucidating the effects of nine-steaming-nine-drying on the morphology, metabolomic profile, and active ingredients of Polygonatum sibiricum Redouté

Background “Nine-steaming and nine-drying” is a pharmaceutical processing technique for Polygonatum sibiricum Redouté. It is an incomplete study that the effect of the method on the quality of P. sibiricum Red. is only evaluated by the changes in the contents of several components. It is necessary to explore the chemical transformations during the nine cycles of steaming and drying of P. sibiricum Red., and the relationship between the chroma and internal chemical compositions. Methods This study investigated the effects of the traditional nine-steaming-nine-drying method on the morphology, metabolomic profile, and medicinal components of P. sibiricum Red. Results Through non-targeted metabolomics analysis, 685 metabolites were identified, with 492 showing differential abundance, particularly amino acids and derivatives, lipids, carbohydrates, and phenols or flavonoids. These alterations resulted in darker coloration, as evidenced by a significant decrease in L* values, elimination of tongue-numbing effects, enhanced sweetness, and improved quality of P. sibiricum Red. The processing resulted in a significant decrease in the relative content of lipids, polysaccharides, oligosaccharides, amino acids and their derivatives, while an increase in flavonoids, saponins, polyphenols, 5-HMF and monosaccharides. The browning of P. sibiricum Red. subjected to steaming and drying mainly correlated with Maillard reaction. Fructose, erucic acid, palmitic acid, linoleic acid, pipecolic acid, L-proline, L-leucine, (5-L-Glutamyl)-L-glutamate, 5-HMF, flavonoids, polyphenols, saponins and flavor compounds, these metabolites and their derivatives can served as the main biomarkers for evaluating the quality of P. sibiricum Red. subjected to steaming and drying. However, excessive steaming and drying caused the bitter and sour flavor intensified, and the quality to deteriorate. Comprehensive analysis revealed that the quality of P. sibiricum Red. was optimal after the seventh cycle of steaming and drying, and the L* value ranged from 21.0 to 22.0, the a * value ranged from 2.0 to 5.0, the C * value ranged from 8.0 to 10.0. Conclusion This research elucidated the mechanisms through which steaming and drying affected the morphology and quality of P. sibiricum Red., established a theoretical foundation for quality assessment of processed P. sibiricum Red.