The effect of water content on the ordered/disordered structures in starches

C-13 cross-polarization magic angle spinning NMR has been used to study the ordered and disordered structures of starches with different water content s. The amorphous regions of starch have been shown to produce NMR patterns only if they are in a glassy state, the widths, positions, and areas of the peaks to some extent being dependent on the temperature and the water cont ent of the starch. In the amorphous region, the peaks were all Gaussian in shape, while the peaks in the ordered regions and Lorentz profiles. Water c ontents in the range 10-50% did not influence the proportion of double heli ces in the starch. Decreasing the water content to 1-3% however, resulted i n a significant decrease in the proportion of double helices, the effect be ing greater than in B- than A-type starches. It is suggested that short-ran ge order structures in starches (double helices) are stabilized by becoming part of long-range order structures (crystallites). (C) 2001 John Wiley & Sons, Inc.