Effect of water sorption on the glass transition temperature and texture of deep-fried models

The purpose of this study was to understand effect of water sorption on the glass transition temperature (Tg) and texture of deep-fried models, namely, bits of deep-fried tempura batter. Two types of deep-fried models (normal and glucose-added samples) were employed. Tg was investigated by thermal rheological analysis (TRA); although TRA measurements for pellet samples showed an unclear glass transition, the measurements for bulk samples showed a large force-drop induced by this effect. Isothermal mechanical relaxation measurement confirmed that the Tg value of the deep-fried samples could be evaluated from the departure point of the force-drop. The Tg decreased with increase in water content because of the water plasticizing effect; the glucose-added sample had a higher Tg than the normal sample at each water content. The fracture property of the samples changed from brittle to ductile at the critical water content and/or water activity (i.e., those at Tg = 25 °C).