Controlling wheat gluten cross-linking for high temperature processing

• Wheat gluten extensively cross-links during aqueous heat treatment at neutral pH.
• Gluten cross-linking is avoided using low pH (<3) during aqueous heat treatment.
• Low pH aqueous heat treatments may be suited to blend gluten with other polymers.

The high temperature blending of wheat gluten with other polymers for the manufacturing of bioplastics is associated with heat induced cross-linking reactions which can increase the viscosity and affect component miscibility. This work showed that a good level of control over the onset of cross-linking can be obtained during heating by adjusting the pH of the environment. Gluten was heated (>100 °C) in buffer solutions of different pH and protein polymerisation was monitored by various methods to assess the extent and nature of aggregation. In a sufficiently acidic environment (pH 2.5–3.0) during heating up to 153 °C, cross-linking was greatly hindered whilst protein degradation was not observed, provided 15 min heating time was not exceeded. Such conditions may well be suited to blend gluten with other polymers at relatively high temperatures in aqueous solvent. When hydrothermally treated gluten samples with large differences in protein cross-linking were compression moulded to produce plastic specimens, little differences in mechanical properties were observed.