NMR local range investigations in amorphous starchy substrates I. Structural heterogeneity probed by C-13 CP-MAS NMR

The C-13 CP-MAS (Cross Polarization and Magic Angle Spinning) NMR signature s of a series of amorphous and semi-crystalline samples prepared from vario us starchy substrates (native potato starch, amylopectin, amylose) followin g different techniques of preparation (casting, freeze drying, solvent exch ange) are compared. Decompositions of the C1 resonance spectra reveal the e xistence of four or five main types of alpha (1-4) linkages, which can be q uantified. The influence of the intrinsic primary structure (linear or bran ched) and of the preparation procedure on conformational changes and result ing crystallinity are interpreted in terms of distributions of average glyc osidic linkages dihedral angles (phi, psi). The role of hydration is also c onsidered. An improved understanding at different structural levels is obta ined in relation to local and intermediate range orders. Such information m ay be useful for the understanding of the structural evolution of a large v ariety of starchy substrates before or after treatments widely used in indu strial processes. (C) 2001 Elsevier Science B.V. All rights reserved.