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.

The change in molecular structure of the soy protein samples as a result of the microbial transglutaminase treatment was studied using solid-state (13)C NMR spectroscopy and circular dichroism (CD), and the relation to the glass transition temperature (T(g)) was examined. From NMR measurements, the structure of the local region of the C(alpha) methine was observed to change, and the region had relatively high mobility. From CD measurements, the structural change seemed to be caused by the change in the secondary structure (disintegration of the beta-structure). By comparison with the T(g) of another protein, the state of the secondary structure of a protein was suggested to be a key in determining its T(g).

Antifreeze activities of various oligo- and poly(amino acid)s, more particularly oligo(glutamic acid)s (OGAs) and poly(glutamic acid)s (PGAs), were measured by differential scanning calorimetry (DSC). The polymers composed of acidic amino acids, such as PGA, had higher antifreeze activity than the other polymers. The antifreeze activities of the OGAs and PGAs tended to decrease as their molecular weights increased. However, their activities in the molecular weight range below 20 000 were higher than the antifreeze activity of glucose, which is known as a highly antifreeze substance. The antifreeze activities were only slightly affected by the optical isomerism and the peptide linkage type and decreased in the order Na salt = K salt ≫ Ca salt ≫ acidic form. It was considered that the high antifreeze activities of OGA and PGA are mainly caused by Coulomb's force of the dissociating counterions. Keywords: Antifreeze activity; oligo(glutamic acid); poly(glutamic acid); molecular weight; counterion