The retrogradation of waxy maize starch extrudates: effects of storage temperature and water content.

The effects of water content and storage temperature on the kinetics of the retrogradation of nonexpanded waxy maize starch extrudates were studied using (1)H pulsed NMR and wide-angle X-ray diffraction. The increase in crystallinity observed by XRD was accompanied by a decrease in the relaxation times of the solid-like component of the NMR free induction and the spin-echo decays, and an increase in the contribution of the solid-like component to the total signal. The dependence of the rate of starch retrogradation on the storage temperature showed the typical "bell-shaped" behavior, which was successfully modeled using the Lauritzen-Hoffman theory of crystallization of chain-folded polymers. This theory was extended to model the effect of water content on the rate of isothermal crystallization by exploiting the ten-Brinke and Karasz, and the Flory equations to describe the dependence of the glass-transition and the melting temperatures on water content. Copyright 2000 John Wiley & Sons, Inc.