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

Abstract

(13)C cross-polarization magic angle spinning NMR has been used to study the ordered and disordered structures of starches with different water contents. 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 content of the starch. In the amorphous region, the peaks were all Gaussian in shape, while the peaks in the ordered regions had Lorentz profiles. Water contents in the range 10-50% did not influence the proportion of double helices in the starch. Decreasing the water content to 1-3%, however, resulted in a significant decrease in the proportion of double helices, the effect being greater in B- than in A-type starches. It is suggested that short-range order structures in starches (double helices) are stabilized by becoming part of long-range order structures (crystallites).