High-temperature compression molding of wheat gluten at low moisture content yields a
rigid, glassy material. Thiol functionalized additives improve the toughness of this material
but the underlying mechanism is not yet fully clear. In order to elucidate the relative
importance of other factors besides cross-linking, wheat gluten was modified by removing
all (disulfide) cross-links in the protein network prior to compression molding. In contrast
with what was the case for molded unmodified gluten, covalent cross-linking in molded
modified gluten (MG) was minimal to non-existent after molding at 130 C. However,
the flexural strength of modified samples was significantly better than that of unmodified
samples. Increasing the molding temperature and thereby altering the degree of cross-linking
in the molded MG network did not have any effect on mechanical properties determined
by both flexural and compression tests. With increasing levels of glycerol, the
decrease in flexural strength and increase in flexural strain was less pronounced for
molded MG than for molded unmodified gluten. We postulate that exposing gluten to
disulfide reducing agents (such as thiol functionalized additives) enhances intermolecular
secondary interactions and increases the number of molecular entanglements, which in
turn contribute to improving the mechanical properties of rigid gluten materials. These
effects are at least as important as chemical (disulfide) cross-links, which some multifunctional
thiol additives may introduce.