Structure and Morphology of Wheat Gluten Films: From Polymeric Protein Aggregates toward Superstructure Arrangements

Abstract

Evaluation of structure and morphology of extruded wheat gluten (WG) films showed WG protein assemblies elucidated on a range of length scales from nano (4.4 Å and 9 to 10 Å, up to 70 Å) to micro (10 μm). The presence of NaOH in WG films induced a tetragonal structure with unit cell parameters, a = 51.85 Å and c = 40.65 Å, whereas NH(4)OH resulted in a bidimensional hexagonal close-packed (HCP) structure with a lattice parameter of 70 Å. In the WG films with NH(4)OH, a highly polymerized protein pattern with intimately mixed glutenins and gliadins bounded through SH/SS interchange reactions was found. A large content of β-sheet structures was also found in these films, and the film structure was oriented in the extrusion direction. In conclusion, this study highlights complexities of the supramolecular structures and conformations of wheat gluten polymeric proteins in biofilms not previously reported for biobased materials.

Structural Changes of Gluten/Glycerol Plastics under Dry and Moist Conditions and during Tensile Tests

“…25 Further thermal treatments can even generate hexagonal close-packed nanostructures (HCP) in WG platics. 25,27,28 Besides the plasticizers, additives, such as acids, bases and urea, have been used to improve the processability of WG. 26,[29][30][31] Interestingly, new tetragonal-packed and HCP nanostructures were discovered in the WG with NaOH and ammonium hydroxide (AH) 28 .…”

Developments in the Science of Zein, Kafirin, and Gluten Protein Bioplastic Materials

“…Such knowledge should enable us to manipulate and direct the process to improve functionality. Literature on protein biomaterials emphasizes the importance of control over inter-and intramolecular weak interactions, and of SS/SH interchange, as these play a profound role defining material performance because they are responsible for arrangement at the macromolecular level (reviewed by Guan 2007;Kuktaite et al 2011). This is referred to as "supramolecular design" and offers the potential to produce bio-plastics, such as those which exist in nature, that have better mechanical properties than synthetic polymers.…”

“…In this regard, Kuktaite et al (2011) describing a model for extruded wheat gluten films, highlighted the complexities of the supramolecular structures and conformations of the wheat prolamins in films and how these are influenced by the film preparation conditions. They identified tetragonal prolamin structures when sodium hydroxide was present in the film forming process, whereas in the presence of ammonium hydroxide, a highly polymerized bidimensional hexagonal structure was formed with glutenins and gliadins intimately mixed.…”

“…Concerning the wheat proteins, Lagrain et al (2010) and Kuktaite et al (2011) stress the importance of disulfide bonding and sulfhydryl-disulfide (SH-S) interchange in the formation and structure of gluten bio-plastics.…”

“…The barrier and mechanical properties of prolamin bio-plastics are presumably a consequence of not just the number of classes and sub-classes of prolamins present, or their contents of hydrophobic amino acids but also the degree of repetition of sequences of amino acids, and related to this the uniformity of their structures (Kuktaite et al 2011). Clearly, because of these factors they are far less uniform in structure than comparable synthetic plastics such as nylon 66 (Morrison and Boyd 1983).…”