Effect of gliadin-glutenin ratio on gluten network formation during thermomolding

Gluten proteins can be applied for producing rigid biobased materials.We studied the effect of the gliadin-glutenin ratio on network formation and on the mechanical properties of the glassy end product after thermomolding.Samples with 7.0% moisture content and without additional plasticizer were processed at 130 and 150 °C for 5 and 25 min.Gluten proteins polymerized during thermomolding and polymerization was faster for glutenin than for gliadin.Gluten polymerization at 130 °C decreases the water absorption of thermomolded gluten.Gliadin-rich samples molded under the same experimental conditions as glutenin-rich samples absorb more water than the latter.The relative contribution of non-disulfide bonds to the gluten network increased with the molding temperature and was higher for glutenin-rich than for gliadin-rich samples.During thermomolding, β-elimination of cystine occurred.Dehydroalanine derived lanthionine cross-links were detected in molded samples in higher levels in glutenin-rich samples than in gliadin-rich samples.The elastic modulus of bioplastic materials, as determined with a 3-point bending test, did not depend on the molding temperature and time at any gliadin-glutenin ratio.However, the modulus increased with increasing gliadin-glutenin ratio.The latter could be related to the higher relaxation enthalpies for the gliadin-rich samples.For glutenin-rich samples the stress at break increased with increasing molding temperature and was correlated with the degree of cross-linking.For gliadin-rich samples the stress at break was independent of the molding conditions.