Authentication of Indian citrus fruit/fruit juices by untargeted and targeted metabolomics

Citrus fruits are one of the most important horticultural crops grown India, and a food commodity that is often targeted for mislabeling worldwide. Authentic citrus fruit samples (Kinnow mandrain (citrus nobilis x Citrus deliciosa), Jaffa and Mosambi orange (Citrus sinensis), and Red blush grapefruit (Citrus paradisi)) were obtained from the Indian Agriculture Research Institute and analysed by an untargeted method using ultra performance liquid chromatography-quadrupole-time of flight mass spectrometry to identify characteristic markers that could potentially be used to control citrus fruit authenticity. The most influential markers identified were: didymin, rhoifolin, isorhoifolin, neohesperidin, hesperidin, naringin, narirutin, limonin glucoside, and vicenin-2. A targeted liquid chromatography-tandem mass spectrometry method was then optimised for the analysis of these markers. Ratios of limonin glucoside to hesperidin, narirutin, and didymin; narirutin to hesperidin and vicenin-2; didymin to hesperidin and narirutin; and vicenin-2 to didymin, have the potential to be used to test for authenticity of Indian citrus fruits/fruit juices and to detect adulteration down to 2%. In addition, using an untargeted qualitative approach and applying PCA, it was possible to discriminate between authentic and adulterated samples (down to 1%), by generation of Cooman's plots.