Comparison of the Metabolites in Fingered Citron Fruit (Citrus medica L. var. sarcodactylis Swingle) and Chayote (Sechium edule) Based on UPLC-Q-Orbitrap MS/MS.

Fingered citron (Citrus medica L. var. sarcodactylis Swingle) is a medicinal and edible citrus fruit cultivated in several major production regions of China. However, comprehensive information on its regional metabolite variation and its chemical differentiation from chayote (Sechium edule), a botanically unrelated commodity that may be confused with fingered citron because of partially overlapping Chinese vernacular names, remains limited. In this study, untargeted UPLC-Q-Orbitrap MS/MS was used to profile fingered citron samples from Zhejiang (CF1), Sichuan (CF2), Guangdong/Guangxi (CF3), and Yunnan (CF4), together with chayote samples used as a targeted authentication comparator (CFM). A total of 380 metabolites were putatively annotated, including 47 secondary metabolites comprising 23 flavonoids, 8 terpenoids, 8 phenols, 3 coumarins, 3 alkaloids, and 2 steroids. Multivariate analyses and hierarchical clustering identified 65 differential metabolites, including 19 secondary metabolites, that clearly separated the five sample groups within the present dataset. The very high cross-validated Q 2 values should nevertheless be interpreted cautiously because of the large taxonomic and metabolic distance between C. medica and S. edule and the limited sample size. The interspecific separation was therefore interpreted as an expected chemotaxonomic difference with practical authentication value, rather than as a comparison between biologically equivalent taxa. Phenylalanine metabolism and flavone and flavonol biosynthesis showed the strongest nominal enrichment, although neither remained significant after FDR correction. These results provide a metabolite reference for regional quality discrimination of fingered citron and identify candidate chemical features for its targeted authentication against chayote. Further validation using independent samples, additional production years, and other potential comparator commodities is required before routine application.