The effect of cross-linking additives on the structure and properties of glassy wheat gluten material

• The compatibility of 3 cross-linkers with rigid gluten material is evaluated.
• Influence of additives on molecular and mechanical properties is studied.
• Modified (cross-link free) gluten is more compatible with the studied additives.
• Thermally activated cross-linkers can selectively cross-link during molding only.

High-temperature compression molding of wheat gluten, an industrial co-product of the manufacture of wheat starch, yields a rigid, glassy gluten material. The improvement of the mechanical properties of this type of material by thiolated additives has been attributed to their simultaneously occurring reducing and/or cross-linking impacts. In this study, three additives with different cross-linking functionalities but which lack reducing properties are tested for their ability to cross-link the gluten network and improve its mechanical properties: glutaraldehyde (DAL), neopentyl glycol diacrylate (DAC) and a retro Diels–Alder based thermally activated cross-linker. The effect of cross-linking on fully reduced disulfide free gluten (MG) was also studied. Both DAL and DAC were able to cross-link (modified) gluten protein during mixing as well as during the molding step while TAC was active during molding. All additives were more effective at cross-linking the MG network than untreated gluten likely due to its higher level of available thiol groups and its less constrained network. However, there was no straightforward link between increased cross-link density and improved mechanical properties. Overall, we postulate that increasing the level of cross-linking in gluten protein can only benefit the mechanical properties when favorable secondary interactions and physical entanglements in the network are retained.

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