Rheological properties of gluten plasticized with glycerol: dependence on temperature, glycerol content and mixing conditions

The rheological behaviour of a gluten plasticized with glycerol has been st udied in oscillatory shear. The mixing operation in a Haake batch mixer lea ds to a maximum torque for a level of specific energy (500-600 kJ/kg) and t emperature (50-60 degrees C) quite independent of mixing conditions (rotor speed, mixing time, filling ratio). The gluten/glycerol dough behaves as a classical gluten/water dough, with a storage modulus higher than the loss m odulus over the frequency range under study. A temperature increase induces a decrease of moduli, but the material is not thermorheologically simple. Glycerol has a plasticizing effect, which can be classically described by a n exponential dependence. Mixing conditions influence the viscoelastic prop erties of the material, mainly through the specific mechanical energy input (to 2000 kJ/kg) and temperature increase (to 80 degrees C). Above 50 degre es C, specific mechanical energy highly increases the complex modulus. The aggregation of proteins, as evidenced by size-exclusion chromatography meas urements, occurs later as the dough temperature reaches 70 degrees C. The n ature of network interactions and the respective influence of hydrophobic a nd disulphide contribution is discussed. A general expression is proposed f or describing the viscous behaviour of a gluten/glycerol mix, which could s eem simplistic for such a complex rheological behaviour, but would remain s ufficient for modelling the flow behaviour in a twin screw extruder.