Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry of Heteropolyflavan-3-ols and Glucosylated Heteropolyflavans in Sorghum [Sorghum bicolor (L.) Moench]

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Abstract
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used to characterize the structural diversity of polyflavans in Ruby Red sorghum [Sorghum bicolor (L.) Moench]. Deionization of the polyflavan fractions with Dowex 50 × 8−400 cation-exchange resin and subsequent addition of cesium trifluoroacetate (133Cs) allowed the detection of exclusively [M + Cs]+ ions. MALDI-TOF MS of the polyflavans that eluate from Sephadex LH-20 columns with methanol and acetone detected a series of masses corresponding to heteropolyflavan-3-ols differing in degree of hydroxylation and nature of the interflavan bond (A-type and B-type). MALDI-TOF MS of the Sephadex−ethanol/methanol (v/v) eluate revealed a series of masses corresponding to heteropolyflavan-5-O-β-glucosides that vary in the extent of hydroxylation and contain a flavanone (eriodictyol or eriodictyol-5-O-β-glucoside) as the terminal unit. The combination of liquid chromatographic separation and MALDI-TOF MS to characterize sorghum polyflavans indicates that the structural heterogeneity is much greater than previously described. Keywords: MALDI-TOF MS; sorghum; polyflavan; polyflavan-3-ol; proanthocyanidin