Microbial Transglutaminase as a Tool to Restore the Functionality of Gluten from Insect‐Damaged Wheat

Abstract

In some wheat‐growing countries, considerable quantities of commercial wheat are rendered unusable in standard baking because of preharvest damage of the grain by protease‐injecting bugs. In the present study, we studied the ability of transglutaminase (TG) treatment of damaged wheat flour to return the functionality of the gluten network. To confirm the TG cross‐linking, the degree of protein hydrolysis, the amount of free thiol groups, and the electrophoresis properties of glutenin subunits were determined. The effectiveness of the TG treatment on insect‐damaged wheat was analyzed by measuring the dough mixing behavior and the gluten quality. A decrease in the degree of hydrolysis (or free amino groups), a reduction in thiol group concentration, and a decrease of extractable high molecular weight glutenin subunits (HMW‐GS) (measured by high‐performance capillary electrophoresis) confirmed the protein cross‐linking catalyzed by TG, the simultaneous formation of disulfide bonds by the proximity of the cross‐linked polypeptide chains, and the formation of aggregates of high molecular weight. The TG treatment of the damaged wheat flour led to a recovery of the consistograph parameters and gluten index value, and the covalent nature of the bonds ensured the stability of the protein changes.

Formation of Homopolymers and Heteropolymers Between Wheat Flour and Several Protein Sources by Transglutaminase‐Catalyzed Cross‐Linking

“…Control samples showed a significant increase (P < 0.05) of the gluten index values after the addition of TG. These results agree with those obtained by Rosell et al (2003) and Bonet et al (2005) when wheat flour was treated with TG. The same effect was observed in the blends of wheat flour and lupin flour, which showed an improvement in gluten quality after the TG treatment, either due to homologous cross-linking within wheat or lupin proteins or the heterologous cross-linking between wheat and lupin proteins.…”

“…Except for the control dough, results for glutenin extractability did not show any significant (P < 0.05) difference between TG-treated and non-TG-treated samples. The decrease in the extractability of the glutenins from TG-treated control flour was mainly due to the formation of large aggregates between the high molecular weight glutenin subunits (HMW-GS) favored by the formation of new covalent bonds and, to a lesser extent, the formation of some aggregates between the low molecular weight glutenin subunits (LMW-GS) (Larre et al 2000;Gerrard et al 2001;Bauer et al 2003a;Mujoo and Ng 2003;Rosell et al 2003;Bonet et al 2005).…”

“…Lately, it has been suggested that TG in baked products may act on gliadin proteins in dough to generate the epitope associated with the celiac response; however, this hypothesis has not been confirmed yet (Gerrard and Sutton 2005). TG has the ability to restore the functional and biochemical properties of damaged wheat or wheat that suffered hydrolysis by proteases (Babiker et al 1996;Bonet et al 2005;Caballero et al 2005). However, the majority of those studies describe the effect of TG generating cross-links in homogeneous protein systems.…”

Immunoreactivity of wheat proteins modified by hydrolysis and polymerisation

“…In turn, the cross-linking of different proteins is a result of transamidation, or a formation of a covalent bond ε-(γ-Q)-K between the ε-amino group of lysine in one protein and γ-carboxamide group of glutamine in another protein [45,46]. TG used in bread technology is responsible for the formation of large insoluble polymers and allows for a modification of the structure of crumb, especially in case of bread produced of poor quality flour or flour containing proteins degraded by insect peptidases [47,48]. Under acidic conditions, TG primarily catalyses reactions of glutamine deamination to glutamic acid [7].…”

Capillary electrophoresis of proteins 2005–2007

“…The effect of transglutaminase addition has been also investigated for the treatment of insectdamaged flour [114]. Glutens from insect-damaged wheat were also analyzed by CZE to elucidate the mechanism of their hydrolytical degradation [115].…”