Magic-Angle ¹³c nmr Study of Wheat Flours and Doughs

Doughs formed from hard- and soft-wheat flours have different rheological properties, which dictate their uses in baking. Cross-polarization, magic-angle spinning (CPMAS) ¹³C NMR spectra of dry, hard- and soft-wheat flours show resolved signals for the starch and protein components of these composites, allowing differences in relative protein contents to be accurately measured. Proton rotating-frame relaxation measurements on these flours show that starch and protein components are phase-separated. CPMAS and Fourier transform (FT) MAS experiments on doughs formed by hydrating flours reveal that added water has little effect on protein signals of half of the hard-wheat flour, while added water causes nearly all of the main-chain protein signals in soft-wheat flour to disappear. Hard- and soft- wheat flour doughs also differ in the relative amounts of small, solubilized sugars and organic acids, which are observed in FTMAS experiments, and in the percentage of total starch that remains solidlike and is detected in CPMAS experiments. These differences are interpreted in terms of plasticization of the macromolecular components of flour by water.