Tangelo and limetta: LC-MS/MS identification and quantification of flavonoid components and antioxidant acivity studies

Citrus –as whole fruits or juices– stand out as key targets of investigation in nutraceutical research, owing to their richness in health-beneficial components and their ubiquitous presence as dietary components. LC-MS is nowadays one of the most efficient tools to unravel the complexity of natural matrices. By applying a reverse phase HPLC-DAD-ESI-MS/MS separation protocol, a large number of flavonoid derivatives (C- or O-glycosyl flavones, flavanones, dihydrochalcones, polymethoxyflavones) and furocoumarins (psoralens) were identified –in a single chromatographic course– in crude citrus juices, and quantified by Selected Reaction Monitoring (SRM). This technique led to the identification in Mediterranean sweet lemon (C. limetta) and tangelo (C. reticulata × C. paradisi) of eight and eleven individual compounds, respectively, nine of which were found for the first time in these fruits (vicenin-2, lucenin-2 4'-methyl ether, orientin 4'-methyl ether, scoparin, rhoifolin and eriocitrin in limetta juice, and lucenin-2, vicenin-2 and narirutin 4'-O-glucoside in tangelo juice). RP-HPLC separation, on a preparative scale, allowed also for a structure-activity relationship study on the flavonoids responsible for the antioxidant properties of tangelo juice: fractions composed of different flavonoid subclasses (C-glycosyl flavones, O-triglycosyl flavanones, O-glycosyl flavones, O-glycosyl flavanones and polymethoxyflavones, respectively) were subjected to DPPH•, O2•–, OH•, ABTS•+ and FRAP assays, shedding light on the relative contribution of these compounds to the total activity of crude tangelo juice.