Effect of crystallinity on the glass transition temperature of starch

The glass transition temperature (T-g) of potato and wheat starches, stored for several periods after gelatinization, was measured by differential scanning calorimetry (DSC), and the relative crystallinity of the starches was measured by X-ray diffractometry. T-g of stored starches was higher than that of starches without storage, and the T-g increment of starches gelatinized at 120 degrees C was higher than that of starches gelatinized at 60 degrees C. The water content at which the glass transition of a starch occurs at 25 degrees C was estimated from DSC data, and it increased linearly with relative crystallinity in two groups that differed in the gelatinization method. These results also showed the quantitative relationship between T-g and retrogradation. In addition, these results suggested that the glass transition of starch could be interpreted in the same way as the glass transition of cross-linked synthetic polymers.