DSC and NMR relaxation studies of starch-water interactions during gelatinization

The interactions between water and starch during gelatinization as affected by water content, maximum heating temperature and amylopectin crystallinity pattern were investigated by Differential Scanning Calorimetry (DSC) and H-1 NMR relaxation. DSC was used to measure additional unfrozen water (AUW) arising from gelatinization, reflecting enhanced water-starch interactions, and enthalpy of gelatinization (DeltaH(gel)) of waxy corn, normal corn, potato and pea starches between 0.7 and 3.0 g water/g dry starch. The contribution of separated G and M1 stages in gelatinization was estimated using a deconvolution DSC technique. The results show that AUW largely depends on the initial water content. For the samples subjected to higher heating temperature (M1 process), a larger AUW is found presumably due to the greater disruption in granule structure. Deconvolution of the biphasic endotherm suggests that, as water content increases, the M1 process is much reduced and gradually incorporates into the dominant G process. NMR T-2 distribution reveals two distinct water populations corresponding to intra- and extra-granular water, which rapidly exchange during gelatinization. After the M1 process, a relatively homogeneous gel with one water fraction from fast diffusional averaging is obtained. AUW and peak T, values of pea starch are intermediate between those of native corn and potato starches, consistent with its composite A- and B-type crystal structure. (C) 2004 Elsevier Ltd. All rights reserved.