Gluten structure

Tilley, K.A., Benjamin, R.E., Bagorogoza, K.E., Okot-Kotber, B.M., Prakash, O., Kwen, H. 2001. Tyrosine cross-links Molecular basis of gluten structure and function. J Agric Food Chem 49 2628-2632. 

Figure 6.1. The role of HMW subunits in gluten structure and functionality. Amino acid sequences derived from direct analysis of purified proteins and the isolation and sequencing of corresponding genes show that the proteins have highly conserved structures, with repetitive domains flanked by shorter nonrepetitive domains containing cysteine residues (SH) available for formation of interchain disulphide bonds. Molecular modelling indicates that the individual repetitive domains form a loose spiral structure (bottom right) while SPM shows that they interact by noncovalent forces to form fibrils (centre right). Includes figures from Parchment et al. (2001) and Humphries et al. (2000).

It is also important to remember that wheat gluten and dough are complex materials, consisting not only of protein and water, but also starch-, lipid-, water- and salt-soluble proteins and smaller carbohydrates, and so on. The properties of these materials and their interactions with the gluten proteins are poorly understood but can be expected to also influence the viscoelastic properties. The challenge therefore is to understand gluten structure at the molecular level and how this structure interacts... 

The fats used in pastry and biscuit confectionery have different functions, which are determined by their rheological properties (plasticity and texture). In pastry, these principal functions are (1) an increase in the plasticity of the pastry (e.g., hard pastry with a low level of hydration) and (2) a break in the body of the pastry (i.e., the fat makes the gluten structure discontinuous, which gives the desired cmmbliness in, for instance, biscuits) (121). 

Figure 2 ESEM images of gluten structure, (a) A featureless surface is seen if the sample is always maintained wet (b) following a protocol akin to that used for conventional SEM imaging, a coarse network structure becomes visible due to the harsh dehydration conditions used (after )...

Figure 14.5 Fully baked tortilla, (a) SEM of cross section of the fully baked disk showing the considerable expansion of the crumb, (b) ESEM illustrating the gelatinization of the starch granules. (c) SEM of the crumb of a dried fully cooked tortilla showing the extensive gluten structure and gelatinized starch.

Reducing agent Chemical compounds (i.e., sodium bisulfite, cysteine) intentionally added to wheat flour in order to break disulfide bonds and weaken the gluten structure. They are mainly used in cookies, cakes, and wheat Hour tortillas. 

If gluten is too loosely distributed in the matrix, then the dough will collapse (structure-property relation)... 

Fig. 9.3 The conceptual schema of micro-macro thinking for the task designing gluten-free com bread, with the explicit use of structure-property relations...

Rye Proteins. While rye is the only European cereal able to completely replace wheat in bread, rye protein is not as effective as wheat protein. One reason for this is that as much as 80% of the protein in a rye sour dough is soluble compared with 10% of soluble protein in a wheat dough. One factor that inhibits the formation of a gluten-like complex is the 4-7% of pentosans present, which bind water and raise the viscosity of the dough. The crumb structure is then formed from the pentosans in combination with the starch. 

The ability of a degradable plastic to decay depends on the structure of its polymer chain. Biodegradable plastics are often manufactured from natural polymers, such as cornstarch and wheat gluten. Micro-organisms in the soil can break down these natural polymers. Ideally, a biodegradable plastic would break down completely into carbon dioxide, water, and biomass within six months, just like a natural material. 

Electrostatic charges due to ionized acidic or basic amino acids influence protein solubility. At extremes of pH, many poorly soluble proteins are dissolved and their molecular structures unfolded due to surplus of similar repelling charges. Gluten proteins have few charged groups and so are poorly soluble in neutral solution (15). Dispersions of other proteins must be adjusted to their isoelectric point or have salt added to optimize cohesion and adhesion. 

High molecular weight and random coil structure of protein result in more associations and thereby enhance adhesive and cohesive properties. Although these characteristics are inherent in native gluten proteins, functional properties of other proteins may be improved by chemical or thermal processing. 

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