Dynamic Variation of Secondary Metabolites from Polygonatum cyrtonema Hua Rhizomes During Repeated Steaming–Drying Processes

Polygonati Rhizoma, widely used as a traditional functional food and herbal medicine, is well known for its health-promoting activities after the process of "nine cycles of steaming-drying". Based on UPLC-MS/MS, 1369 secondary metabolites were identified in <i>P. cyrtonema</i> rhizomes, mainly alkaloids, amino acids and derivatives, flavonoids, organic acids, phenolic acids, and saccharides. The <i>P. cyrtonema</i> rhizomes were rich in xylose, arabinose, glucose, sorbose, mannose, galactose, rhamnose, inositol, fucose, sedoheptulose, phosphorylated monosaccharides, sugar acid, and sugar alcohols. Particularly, 23 types of modifications were detected for amino acids, while the most frequent modifications were acetylation, methylation (nono-, di-, and tri-), cyclo-, homo-, and hydroxylation. Based on the metabolic profile, samples from the third cycle (Tre-3) and the sixth cycle (Tre-6) were firstly clustered together due to similar metabolites and then grouped with samples from the ninth cycle (Tre-9). Differentially accumulated metabolites were mainly enriched in "Metabolic pathways", "Biosynthesis of cofactors", "Biosynthesis of secondary metabolites", "Flavonoid biosynthesis", "Purine metabolism", "ABC transporters", "Biosynthesis of amino acids", and "Nucleotide metabolism" pathways. During repeated steaming-drying processes, 39 metabolites occurred, including alkaloids, amino acids and derivatives, flavonoids, lignans and coumarins, lipids, nucleotides and derivatives, organic acids, phenolic acids, and terpenoids. This research will provide a critical scientific basis for postharvest processing of <i>P. cyrtonema</i> rhizomes.