EFFECT OF CRYSTALLINITY ON THE GLASS-TRANSITION TEMPERATURE OF STARCH

The glass transition temperature (T-g) of potato and wheat starches, s tored for several periods after gelatinization, was measured by differ ential scanning calorimetry (DSC), and the relative crystallinity of t he starches was measured by X-ray diffractometry. T-g of stored starch es was higher than that of starches without storage, and the T-g incre ment of starches gelatinized at 120 degrees C was higher than that of starches gelatinized at 60 degrees C. The water content at which the g lass 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 star ch could be interpreted in the same way as the glass transition of cro ss-linked synthetic polymers.