Abstract
Wheat and potato starches were hydrolysed with 2·2 n hydrochloric acid at 35°C for a period of time up to 15 days. The residues (lintnerised starches) were washed and freeze dried, and studied by differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), small-angle light scattering (SALS), small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS). These techniques showed that profound changes took place in the first day of hydrolysis (during which time the extent of hydrolysis was 7·7% for potato starch and 12·5% for wheat starch). In particular, the gelatinisation enthalpy (ΔH) decreased, the X-ray crystallinity increased and the SANS and SAXS peaks (indicative of a regular spacing between crystalline and amorphous regions) virtually disappeared. The reduction in ΔH is surprising and is discussed at length. It was also shown that freeze drying results in a considerable lowering of the gelatinisation temperature of potato starch (and also of ΔH) while that of wheat starch is only slightly affected.
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