抄録
An attempt was made to follow the changes in macro-and microscopic states of starch granule-in-water systems during gelatinization due to heating. A microscopic examination, DSC measurement and observation of the mechanical responses under a small stress were conducted to examine the effect of gelatinization of the starch components on the rate of increase of the internal temperature of foodstuffs during cooking. It was confirmed that the starch granules from potato and wheat showed a much higher degree of swelling in the corse of gelatinization than those from glutinous and non-glutinous rices and corns. However, the results obtained from DSC measurement indicated that the apparent heat of gelatinization was highest with potato starch (-27.3mJ) among the samples tested, while that for wheat starch was the lowest (-15.2mJ). The mechanical responses to a low stress, i. e. instantaneous elasticity and steady flow viscosity, were characterized by a type of convex curves according to the progress of gelatinization for all the samples tested. These responses started to increase at the beginning of gelatinization, attained maximal values at around 70°C corresponding to disappearance of the crystal region in the starch molecules, and finally tended to decrease with further temperature increase.
The results obtained from this study will be utilized in future work to examine the effect of gelatinization on the increase of internal temperature of foodstuffs during cooking.
