SOLID-STATE NMR-STUDIES ON THE STRUCTURE OF STARCH GRANULES

Resonances expected for carbon atoms in the amorphous regions of moist ened starch granules are not visible in C-13 CP/MAS NMR spectra. These resonances could be observed in spectra obtained by using a single-pu lse, Bloch-decay sequence, with magic-angle spinning (SP/MAS). This im plies that the amorphous regions in moistened starch granules are mobi le and have properties similar to a rubberlike polymer. For moistened wheat starch granules, proton rotating frame relaxation times for reso nances assigned to the amylose-lysophospholipid inclusion complexes we re shorter than those of the crystalline starch. Relaxation difference s were used to generate subspectra of the crystalline starch and the a mylose-lysophospholipid inclusion complex. Our results suggest that th e inclusion complexes occur in distinct regions of the starch granule. There are thus three distinct components making up the wheat starch g ranule: (i) highly crystalline regions farmed from double-helical star ch chains, (ii) solid-like regions formed from lipid inclusion complex es of starch, and (iii) completely amorphous regions, associated with the branching regions of the amylopectin component of starch and possi bly the lipid-free amylose. All these components can be observed separ ately using different solid-state NMR techniques and would be expected to contribute to the physical properties of a wheat starch granules.