Why Wholemeal Flour Has Higher Protein But Produces Smaller Bread Volume.
Wholemeal flour is often associated with higher protein content than white flour, yet, its bread typically exhibits a smaller volume.
1️⃣ PROTEIN DISTRIBUTION IN WHEAT GRAIN
– The wheat grain is composed of different layers, including the starchy endosperm, the aleurone layer, and the outer bran layers.
– Protein is not uniformly distributed throughout the grain; the central endosperm, the primary source of white flour, contains a lower protein concentration but a higher starch content.
– Wholemeal flour, retains all parts of the grain, resulting in a higher overall protein content. However, not all proteins contribute equally to gluten formation.
2️⃣FUNCTIONAL VS. NON-FUNCTIONAL PROTEINS.
– Gluten, essential for dough elasticity and gas retention, is primarily formed from gliadin and glutenin in the endosperm.
– Wholemeal flour contains extra proteins from the bran and aleurone layers, they do not contribute to gluten formation. Despite higher protein content, wholemeal dough has weaker gluten strength.
3️⃣ BRAN INTERFACE IN GAS RETENTION
– The presence of bran is a key factor in the reduced volume of wholemeal bread. Bran particles introduce discontinuities in the gluten network, weakening its ability to trap gas.
– Theories suggest that bran may physically puncture gas cells or act as sites of weakness where gas bubbles coalesce and escape during fermentation and baking.
– Bran competes with gluten for water absorption, leading to reduced dough extensibility and elasticity.
4️⃣ MILLING AND FORMULATION ADJUSTMENTS
– Given these challenges, wholemeal bread formulations often include high-protein wheat or added vital wheat gluten to compensate for the disruptive effects of bran.
– Even so, the gas retention efficiency of wholemeal dough remains lower than that of refined white flour, necessitating modifications in mixing time, hydration levels, and fermentation techniques to optimize loaf volume.
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