Abstract
It is practically important to understand glass transition temperature (Tg) of dry food products for their quality control. Tg of food products has been often investigated by using differential scanning calorimetry (DSC). However, there is little report on Tg of cookie products. This may be because DSC thermogram shows intricate thermal response. In order to understand Tg of cookie, thermal rheological analysis (TRA) which has a similar principle to thermal mechanical analysis was established, and softening behavior of cookie related to glass transition was investigated. Preliminarily, inulin was employed as a standard material, and relationship between Tg and softening temperature (Ts) was investigated. Glass transition and softening of inulin sample were clearly observed by DSC and TRA, respectively. The Ts was directly proportional to the Tg. On the other hand, cookie sample showed no apparent glass transition in the DSC thermogram, but TRA showed clear softening reflecting glass transition. The Ts decreased with increase in the water content because of plasticizing effect of water. This result was useful for prediction of the water content which cookie softens at room temperature.
