Normal corn starch containing 25 or 30% moisture and potato starch containing 20 or 25% moisture were heat-moisture treated at 120°C for 1 h and the changes in thermal transition characteristics and gel properties of the starches were examined. Granular crystallinity on X-ray diffractogram, especially for potato starch, was reduced by the heat-moisture treatment (HMT). At a limited moisture content (15% based on total weight), Tg measured in granular form of starch decreased by 2-6°C. At Tg, the change in heat capacity (∆CP) of the treated starch was substantially higher than of the corresponding native starch. Crystal melting of the heat-moisture treated starches, measured at 80% moisture, appeared to be biphasic on a DSC thermogram, in that the original endotherm became smaller while a new endotherm at higher temperature was enlarged by the HMT. However, the total melting enthalpy for starch decreased, indicating a partial loss of crystallinity. The degree of rétrogradation under DSC was not significantly different between the native and treated starches. The HMT starches formed the gel with more opaqueness and brittleness. The gel stability from freeze-thawing treatment was slightly increased with corn starch, but decreased with potato by the HMT. Overall results on the paste viscosity and gel properties indicated that the HMT provided physical cross-linking effects on starch.
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