14E-39 |
Tandem mass spectrometry of citrus limonoids |
Q. TIAN and S. J. Schwartz. Dept. of Food Science & Technology, Ohio State Univ., 2015 Fyffe Ct., 110 Parker Food Science Bldg., Columbus, OH 43210-1007 Citrus limonoids are an important group of complex triterpenoids present in Rutaceae and Maliaceae families in aglycone and glucoside forms. Recent studies have shown that citrus limonoids possess important biological activities such as anticancer activity in laboratory animals, inhibition of cancer cell proliferation, induction of apoptosis of human breast cancer cells and phase II enzymes activity enhancement in animal models. The limited availability of limonoid standards and the lack of characteristic UV/vis absorption spectra have often made the characterization of limonoids a challenge to food analytical chemists. In this research, we present the first application of tandem mass spectrometry (MS-MS) for the analysis and characterization of citrus limonoid aglycones and glucosides. Fragmentation patterns of different limonoid aglycones and glucosides can be used to unequivocally identify limonoids present in citrus products and citrus seed extracts exhibiting biological activity. Negative-ion atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS/MS) and positive-ion electrospray ionization (ESI) tandem mass spectrometry (MS-MS) with low-energy collisionally-activated dissociation (CAD) were used to characterize the fragment ions of four limonoid aglycones and six glucosides. Ammonium hydroxide or acetic acid was used to facilitate ionization. After collisionally activated-dissociation of limonoid aglycone molecular ions, structural information of the precursor ions was obtained from the fragments, indicating the presence of methyl, carboxyl, and oxygenated structure of the rings. Positive-ion collisional activation of the limonoid glucosides yielded the molecular ion information of the corresponding aglycones. Application of this MS/MS method is shown for the analysis of citrus juices and grapefruit seed extracts, identifying the presence of nomilin glucoside and obacunoic acid glucoside. In conclusion, tandem mass spectrometry with fragmentation patterns observed in the CAD spectra can be used as important references for structural determination and positive identification of limonoids and represents a powerful analytical tool for further study in this field.
Session 14E, Nutraceuticals & Functional Foods: General I
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