Relationship between the glass transition temperature and the melt flow behavior for gluten, casein and soya

The effects of moisture content (25–45% wwb) and temperature (75–120 °C) on the viscosity of gluten, soya and rennet casein systems was studied using a capillary rheometer. An attempt was made to relate the viscosities to the glass transition temperature measured by differential scanning calorimetry, dynamic mechanical thermal analysis and the phase transition analyzer. The temperature where the material flowed was also determined by the latter technique. All three-protein systems showed shear and extension thinning. Over the shear rate range investigated (∼1–103 s−1), gluten had a substantially lower viscosity than the other two proteins, although the difference was less pronounced at the highest temperature studied. This low viscosity is reflected by lower values of the glass transition temperature, the melt flow temperature and the dynamic moduli E′ and E″ in the rubbery state. The results are discussed in terms of the structure and heat induced changes for the three proteins and their relevance to food processing considered.