Molecular mobility of polysaccharide chains in starch investigated by two-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 of molecular motion of the polysaccharide chains on a time-scale of seconds was found. Molecular motion of polysaccharide chains during retrogradation on a time-scale of milliseconds was clearly visible from line broadening in the one-dimensional spectra. The spectra indicated motions with correlation time (tau(c)) of about 100 mu s. Ultraslow motions with tau(c) of tens of milliseconds were detected with stimulated echo and two-dimensional exchange NMR. Results showed that the retrogradation process occurs with a very wide distribution of correlation times. This NMR approach can be used in studies examining molecular mobilities in a wide range of complex and polymeric materials in relation to their physico-chemical properties and behaviour. (C) 1997 Published by Elsevier Science Ltd. All rights reserved.