Effect of glass transition on the hardness of a thermally compressed soup solid

This study described the effect of water content on the glass transition temperature (T-g) of a soup powder and the hardness of a soup solid compressed at various temperatures above and below the T-g. Although differential scanning calorimetry showed indistinct glass transition, thermal rheological analysis revealed a clear mechanical glass transition. The mechanical T-g decreased as water activity (or water content) increased because of a water-plasticizing effect. Since X-ray diffraction showed peaks reflecting crystalline NaCl, lactose, and sucrose, the amorphous region in the soup powder likely consisted mainly of vegetable, yeast, beef, and chicken extracts. The fractural stress of the thermally compressed soup solid increased with water activity of the samples, compressed height (density), and temperature. The results showed that the fractural stress of the soup solid increased dramatically when it was compressed at a temperature above the mechanical T-g.