Mechanism of gliadin–glutenin cross-linking during hydrothermal treatment |
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Authors: | Bert Lagrain Bert G ThewissenKristof Brijs Jan A Delcour |
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Affiliation: | Laboratory of Food Chemistry and Biochemistry, Katholieke Universiteit Leuven, Kasteelpark Arenberg 20, B-3001 Leuven, Belgium |
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Abstract: | 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 μmol/g protein) and the reducing agent dithiothreitol (DTT, 6.1 μmol/g protein) were added to 20% (w/w) gluten-in-water suspensions at room temperature, at 90 °C and after 15 min at 95 °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 α- and γ-gliadin and this decrease was independent of the time of addition during hydrothermal treatment. In contrast, potassium iodate increased the levels of extractable α- and γ-gliadin. Its impact was less when added at later times during RVA analysis. A SH-blocking agent (N-ethylmaleimide, 8.0 μmol/g protein), added at room temperature to the gluten suspension, decreased RVA viscosity at 95 °C and increased the extractabilities of glutenin and α- and γ-gliadin after hydrothermal treatment. Subsequent addition, at 90 °C, of a reducing agent (glutathione, 3.1 and 6.2 μmol/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. |
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Keywords: | db dry basis DTT dithiothreitol GSH glutathione HPLC high performance liquid chromatography NEMI N-ethylmaleimide RP reversed-phase SDS sodium dodecyl sulfate SE size-exclusion SH sulfhydryl SS disulfide |
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