A comparative metabolomic investigation in fruit sections of Citrus medica L. and Citrus maxima L. detecting potential bioactive metabolites using UHPLC-QTOF-IMS

The current study focused on targeted and non-targeted metabolomics of Citrus fruit parts (exocarp, mesocarp, endocarp, and seeds) to gain a comprehensive metabolomic insight. Sections of the Citrus fruit were preliminarily examined for proximate compositions (moisture, ash, fibre, fat, and protein). Whereas ultrasonication-assisted solvent extraction revealed a higher phenolic and flavonoid content at 80% (v/v) ethanolic medium, with the highest amount in the exocarp. Using targeted metabolomics, hesperidin (3307.25 mg/100 g), naringin (4803.73 mg/100 g) were detected in C. medica and C. maxima at greater levels, respectively. Further quantitative analysis revealed the presence of phenolic acids (gallic acid, trans-ferulic acid, p-coumaric acid, trans-cinnamic acid), and polymethoxyflavones (nobiletin, and tangeretin) and detected in the order of exocarp > mesocarp > endocarp > seeds. Using an untargeted metabolomics approach, metabolite discriminations among Citrus fruit sections were illustrated by Venn-diagram, heatmap, PCA, o-PLSDA, correlation matrices, and S-plot. UHPLC-QTOF-IMS revealed 48 metabolites including phenolics, vitamins, and amino acids. Furthermore, the METLIN database leads to the identification of 202 unknown metabolites. The metabolite biosynthesis and corresponding metabolite presence in Citrus fruit sections were confirmed using pathway enrichment and mass fragmentation analysis. Finally, potential biological activities were determined using in silico PASS software approach, and free radical scavenging potential was confirmed using in vitro assays for future preventive and therapeutic applications of the identified metabolites.