Crystallinity and structuring role of water in native and recrystallized starches by 13C CP-MAS NMR spectroscopy 1: Spectral decomposition

Amorphous, native, and recrystallized starches were studied by 13C CP-MAS NMR spectroscopy with respect to their behavior with hydration. The study of space groups, associated to crystalline polymorphs (B2 and P61 for A and B forms, respectively), provided decomposition rules for the spectral part due to crystalline phases. Moreover, the subtraction of a standard amorphous spectrum apparently showed the existence of three phases in native starches (amorphous, partially-ordered and crystalline) and only two in spherulitic crystals (partially-ordered and crystalline). The proportion of each phase was estimated at two different hydration levels. The amount of crystalline phase was compared to the degree of crystallinity as evaluated by wide angle X-ray scattering. The NMR spectral changes with hydration could be interpreted in terms of two complementary roles of water molecules, i.e. structuring and plasticizing.