Key metabolic pathways of the aging process of Citri Grandis Exocarpium and its identified potential metabolites associated with antioxidant activity

Citri Grandis Exocarpium (CGE), is renowned for its dual use in medicine and food, being well-known for its beneficial antioxidant and anti-inflammatory effects. However, the changes of chemical composition and antioxidant activity of CGE during the storage (aging) process are still unclear. In this study, We examined the changes in metabolites of CGE samples aged for 1 year (CG1), 3 years (CG3) and 5 years (CG5), mainly through comprehensive metabolomics techniques. The results indicated that analysis of CGE extracts by ultra-high-performance liquid chromatography-quadrupole/time of flight mass spectrometry (UHPLC-QTOF-MS/MS) resulted in the detection of 1249 metabolites. A total of 57 differential metabolites were identified as potential markers for distinguishing CGEs of different aging years by chemometrics methods, including naringin, among others. The KEGG annotation, enrichment and topology analysis revealed that the biosynthesis of flavonoids was a key metabolic pathway during the aging process of CEG, involving 14 flavonoids determined as differential metabolites. Total flavonoids, naringin, naringenin, butin, 7',4-dihydroxyflavone, and phlorizin have been identified as potential metabolites associated with antioxidant activity. These results clarified the effects of aging time on the flavonoids accumulation and antioxidant activity of CGE, and provided a scientific basis for understanding the mechanism of CGE aging process.