The gluten proteins, gliadin and glutenin, are important for wheat flour functionality and they undergo changes during heat treatment involving sulfhydryl (SH) groups. To change the level of SH-groups during hydrothermal treatment, the oxidant, potassium iodate (2.1 mu mol/g protein) and the reducing agent dithiothreitol (DTT, 6.1 mu mol/g protein) were added to 20% (w/w) gluten-in-water suspensions at room temperature, at 90 degrees C and after 15 min at 95 degrees C, and the viscosity was measured by the Rapid Visco Analyser (RVA). Protein extractabilities after hydrothermal treatment were determined by size-exclusion and reversed-phase HPLC. DTT decreased maximal RVA viscosity and the levels of extractable alpha- and gamma-gliadin and this decrease was independent of the time of addition during hydrothermal treatment. In contrast, potassium iodate increased the levels of extractable alpha- and gamma-gliadin. Its impact was less when added at later times during RVA analysis. A SH-blocking agent (N-ethylmaleimide, 8.0 mu mol/g protein), added at room temperature to the gluten suspension, decreased RVA viscosity at 95 degrees C and increased the extractabilities of glutenin and alpha- and gamma-gliadin after hydrothermal treatment. Subsequent addition, at 90 degrees C, of a reducing agent (glutathione, 3.1 and 6.2 mu mol/g protein) recovered the control RVA profile and restored the control protein extractabilities after RVA analysis. This shows the importance of heat-induced gliadin-glutenin reactions for gluten viscosity and of the presence of free SH-groups for the polymerization of gluten proteins. A model explaining gliadin-glutenin polymerization through a sulfhydryl-disulfide exchange mechanism and demonstrating the effects of redox agents is put forward. (C) 2007 Elsevier Ltd. All rights reserved.