Andreas Redl

Heat and shear mediated polymerisation of plasticized wheat gluten protein upon mixing

Abstract The relative influence of mechanical and thermal energy inputs experienced by plasticized wheat gluten upon mixing was evaluated. Changes in the gluten network structure was assessed through rheological and biochemical characterisation. Gluten was mixed with glycerol in a thermostated counterrotating batch mixer recording torque and temperature. The mixer was thermostated at 40, 60 and 80 °C and the mixing time varied from 2 to 30 min at constant mixing speed (100 rpm) in order to obtain samples with different thermal and mechanical energy histories. Rheological properties were investigated in oscillatory shear mode and the obtained mechanical spectra were quantified using Cole–Cole distributions. Size distribution of the total gluten protein was studied by size-exclusion-HPLC. Results evidenced an increasing gluten protein polymerisation with sample temperature, a phenomenon already documented. Time-temperature superposition of torque curves and kinetic modelling of protein solubility loss allowed the calculation of an apparent energy of activation of 33.7 kJ/mol for the rheological and biochemical changes upon mixing. This value is far from the more than 100 kJ/mol usually reported for gluten polymerisation reaction upon heating. In the light of this discrepancy the catalytic role of shear stress is discussed.

Wheat Proteins as Polymeric Materials: Rheological Properties of Plasticized Gluten

Shaping with extrusion technology is of major importance for succesful implementation of “bioplastics”. This requires a good knowledge of the materials viscous behaviour. The aim of the present paper is to characterize the rheological properties of commercial gluten plasticized with glycerol, in order to better understand its structure and flow properties and to derive a phenomenological equation.