MOLECULAR MOBILITY OF POLYSACCHARIDE CHAINS IN STARCH INVESTIGATED BY2-DIMENSIONAL SOLID-STATE NMR-SPECTROSCOPY

Slow molecular motion of polysaccharide chains in native starch and in retrograding starch gels was investigated by one-and two-dimensional exchange solid-state NMR spectroscopy. In native starch, no evidence o f molecular motion of the polysaccharide chains on a time-scale of sec onds was found. Molecular motion of polysaccharide chains during retro gradation on a time-scale of milliseconds was clearly visible from lin e broadening in the one-dimensional spectra. The spectra indicated mot ions with correlation time (tau(c)) of about 100 mu s. Ultraslow motio ns with tau(c) of tens of milliseconds were detected with stimulated e cho and two-dimensional exchange NMR. Results showed that the retrogra dation process occurs with a very wide distribution of correlation tim es. This NMR approach can be used in studies examining molecular mobil ities in a wide range of complex and polymeric materials in relation t o their physico-chemical properties and behaviour. (C) 1997 Published by Elsevier Science Ltd. All rights reserved.