Characterization of flavone C-glycosides and phenolic compounds in tara (Caesalpinia spinosa) seed germ flour by HPLC coupled with high resolution mass spectrometry

The cotyledon or germ of tara (Caesalpinia spinosa, Fabaceae family) is a protein- (45 %, w/w) and polyphenolrich (14.9 g kg 1) co-product of the extraction of tara seed gum (E417). In this work, the polyphenols of tara seed germ (TSG) were comprehensively characterized for the first time using HPLC-diode array detector and nanoflow HPLC coupled with high-resolution tandem mass spectrometry (MS/MS) in switching polarity ion mode and stepped collision energy. Apigenin di-C-glycoside derivatives were the largely predominant phenolic compounds of TSG. The concentrations of vicenin-2, vicenin-1 and vicenin-3 were 6.7, 1.4 and 1.5 g kg􀀀 1, respectively, as determined by HPLC-UV. Several complex flavone C-glycoconjugates, O-glycosyl-C-glycosyl mixed derivatives and O-acylated-di-C-glycosides, among which benzoylated vicenin-2, were putatively assigned based on MS/MS spectra. The applied MS method was particularly effective to distinguish between possible isomeric acylated derivatives and to confirm their structural difference from multi-glycosylated isobaric compounds. Arguably, TSG is the richest source of flavone C-glycosides described so far. Because of its content of macro- and micronutrients, TSG is a multifunctional food ingredient obtained from co-products of neglected species although its safety profile remains to be assessed. In the meanwhile, pinpointing the phenolic compounds of TSG offers a valuable analytical reference for its monitoring.