Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry of Polygalloyl Polyflavan-3-ols in Grape Seed Extract

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Abstract
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was employed to characterize the polygalloyl polyflavan-3-ols (PGPF) in grape seed extracts. Masses corresponding to a series of PGPF units inclusive of nonamers were observed in the positive-ion reflectron mode. Masses of PGPF inclusive of undecamers were observed in the positive-ion linear mode, providing the first known evidence of PGPF of this size. Soluble PGPF of grape seed extracts were precipitated by complexation with Yb3+. The PGPF were then recovered by dissolving the precipitate in water and removing the Yb3+ by a weakly acidic cation-exchange resin (Amberlite IRP-64). Comparisons of HPLC chromatograms of the crude grape seed extract prior to precipitation with Yb3+ and after recovery of the PGPF indicated that 96% of the phenolic compounds were precipitated and 99% of the precipitated PGPF were recovered by cation-exchange resin. These results indicate that MALDI-TOF MS is able to determine the mass distribution of complex mixtures of oligomeric PGPF and that precipitation of PGPF by Yb3+ is useful for isolation and quantification. Keywords: MALDI-TOF MS; grape seed; proanthocyanidins; ytterbium