Define Changes in Gluten Proteins during Dough Formation?

Initially, gluten is formed when flour and water are mixed together. The proteins in the flour, glutenin and gliadin cross link, using water as a vehicle to form gluten. Enhancing this gluten structure is important relative to developing a gas retaining structure in the chapati/bread. When the hydrated bread flour is mixed and kneaded, the gluten proteins orient themselves aligns and partially unfolded. This enhances hydrophobic interaction and formation of disulphide bridges through -S-S- interchange reactions. A 3-dimensional viscoelastic protein network is established, as the initial gluten particles transform into this membrane (film), thus serving to entrap starch granules and other flour components. Cleavage of disulphide bridges by reducing agents such as cysteine, destroys the cohesive structure of hydrated gluten and bread dough ; the addition of agents such as bromates, increase toughness and elasticity. "Strong" flours from certain wheat varieties require long mixing time and give very cohesive dough. "Weak flours" are less effective and gluten network breaks down when the energy or duration of mixing exceeds a certain level, probably because of -S-S- bonds are ruptured (especially in absence of air). Dough strength appears to be related to a large content of high molecular weight glutenins including totally insoluble "residue proteins". From experiments with "reconstituted" wheat flours of varying gliadin and glutenin ratios, it can be postulated that the glutenins are responsible for the elasticity, cohesiveness and mixing tolerance of dough whereas gliadins facilitate fluidity, extensibility and expansion of the dough, thus contributing to a larger bread loaf volume. A proper balance of the proteins is essential for bread making. Excessive cohesion (glutenins) inhibit the expansion of trapped CO₂ bubbles during fermentation, the rise of the dough and the subsequent presence of open air cells in the bread crumb. Excessive extensibility (gliadins) results in gluten films that are weak and permeable; thus retention of CO₂ is poor and dough collapse may occur.