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 us ing H-1 pulsed NMR and wide-angle X-ray diffraction. The increase in crysta llinity observed by XRD was accompanied by a decrease in the relaxation rim es of the solid-like component of the NMR free induction ann the spin-echo decays, and an increase in the contribution of the solid-like component to the total signal. The dependence of the rare of starch retrogradation on th e 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 Ir as extended to model the effect o f water content on the rare of isothermal crystallization by exploiting the ten-Brinke and Karasz, and the Flory: equations to describe the dependence of the grass-transition and the melting temperatures on water content. (C) 2000 John Wiley & Sons, Inc.