Phenolic compounds and quantitative 1H-NMR spectroscopy for authentication of lemon, lime, orange, and grapefruit juices

Reliable authenticity and quality assessments of Citrus juices are of paramount importance for sustaining consumer confidence and fair-trade practices. In this study, we investigated two authentication techniques, i.e., ¹H-NMR spectroscopy and HPLC-DAD analyses individually and in combination. Targeted ¹H-NMR spectroscopy was employed to determine concentrations of major constituents of orange, grapefruit, lemon, and lime juices including sugars, organic, and selected amino acids. HPLC-DAD analyses yielded levels of selected minor components, i.e., phenolic compounds, coumarins, and psoralens. Therefore, the combined use of both analytical methods permitted a comprehensive evaluation of the chemical composition of the juices, enabling a clear-cut species-related differentiation. In addition to the confirmation of some established markers, the consideration of novel minor constituents was proposed to support reliable differentiations of the above Citrus juices for improved future authenticity analyses.