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

• Published in: Journal of food engineering Vol. 247; pp. 38 - 44
• Main Authors: Mochizuki, Takumi, Sogabe, Tomochika, Hagura, Yoshio, Kawai, Kiyoshi
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2019
• Subjects: Glass transition temperature; Hardness; Soup powder; Thermal compression; Thermal rheological analysis; Soup powder; Thermal rheological analysis; Hardness; Glass transition temperature; Thermal compression
• ISSN: 0260-8774; 1873-5770
• DOI: 10.1016/j.jfoodeng.2018.11.019

This study described the effect of water content on the glass transition temperature (Tg) of a soup powder and the hardness of a soup solid compressed at various temperatures above and below the Tg. Although differential scanning calorimetry showed indistinct glass transition, thermal rheological analysis revealed a clear mechanical glass transition. The mechanical Tg 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 Tg. •Tg of the soup powder samples could be evaluated by thermal rheological analysis.•DSC thermograms showed endothermic peaks due to the melting of fat.•X-ray diffraction identified crystalline NaCl, lactose and sucrose.•Fractural stress of the soup solid increased when it was compressed above the Tg.•Fractural stress of the soup solid increased with sample density.