Large-scale profiling of alkaloids and related nitrogenous metabolites in cultivated and wild citrus germplasm resources.

Citrus fruits are rich in bioactive alkaloids with significant potential for functional food development. In this study, a targeted TOF performance liquid chromatography mass spectrometry (UPLC-Q-TOF-MS) method was established for the detection of alkaloids and related nitrogenous metabolites. We analyzed the contents of 10 quantified compounds in 87 citrus germplasm resources and characterized the quantified compounds accumulation patterns across multiple tissues and developmental stages in representative varieties. L-pipecolic acid was the predominant nitrogenous metabolite, accounting for more than 80% of the quantified compounds, while synephrine and stachydrine accumulated preferentially in sweet orange (Citrus sinensis), sour orange (Citrus aurantium L.), and mandarin (Citrus reticulata Blanco). Additionally, a decreasing trend in the content of the 10 quantified compounds was observed along with citrus fruit ripening. These findings support the screening of high-alkaloid citrus varieties, optimization of harvest timing for functional compound extraction, and high-value utilization of citrus peel by-products in food applications.