Aging Mechanism of Pericarpium Citri Reticulatae ‘Chachiensis’ during in situ Storage Based on Widely Targeted Metabolomics and High-Throughput Sequencing

This study explored the mechanism of the differences in quality between in situ and non-in situ stored Pericarpium Citri Reticulatae ‘Chachiensis’, commonly known as Guangchengpi (GCP) in Chinese. Using widely targeted metabolomics and high-throughput sequencing, we analyzed the changes in metabolites and microbial communities in GCP during in situ (Guangdong) and non-in situ (Beijing, Sichuan, and Yunnan) storage. The results showed that ultra-high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) identified and characterized 1 440 metabolites, 472 of which were selected as differential metabolites. Compared with the other storage locations, all differential flavonoid metabolites identified in the samples stored in Guangdong were up-regulated, the flavonoid synthesis pathways were significantly enriched, and the total flavonoid content was significantly higher. Fourteen flavonoid metabolites upregulated in the Guangdong samples were identified as key metabolites in the aging process of GCP. Aspergillus and Sphingobium were significantly enriched in the Guangdong samples. Correlation analysis showed that the average temperature was significantly positively correlated with key differential metabolites (P < 0.05). Aspergillus, Cutibacterium, Staphylococcus, Xeromyces, Entyloma showed significantly positive correlations with the key metabolites 6-methoxykaempferol-3-O-glucoside, 2’,3’,4’,5,7-pentahydroxyflavone, skullcapflavone II, quercetin and chrysoeriol-7-O-gentiobioside (P < 0.05). Aspergillus and Xeromyces were selected as the core microorganisms during the aging process. In conclusion, the average temperature, as a significant factor affecting the quality of GCP, induces the enrichment of core microorganisms such as Aspergillus and Xeromyces, thus accelerating the accumulation of flavonoid compounds in GCP stored in situ. This study provides a scientific basis for elucidating the significance of in situ storage of GCP and gaining insights into its aging mechanism.