A DIFFERENTIAL SCANNING CALORIMETRY STUDY OF MELTING TRANSITIONS IN AQUEOUS SUSPENSIONS CONTAINING BLENDS OF WHEAT AND RICE STARCH

Differential scanning calorimetry (dsc) has been used to study the transitions that take place when an aqueous suspension containing a blend of wheat and rice granules is heated. These starch types gelatinize over distinctly different temperature ranges. The positions of the wheat and rice endotherms in the dsc traces are governed by the melting of granules of different stabilities at different volume fractions of diluent. When the total concentration of starch in the suspensions is relatively low, that is less than about 30% wt, the dsc traces for the blends are simply the sum of the outputs for each of the components in the mixture. However, at higher starch concentrations competition for water occurs and non-additive behaviour is found. Under these conditions the wheat starch, since it gelatinizes first, has access to more water and melts at about the same temperature as controls. The rice granules give an endotherm at higher temperatures than controls since the gelatinized wheat particles have already absorbed much of the aqueous phase.