Effect of Heat Treatment and Particle Size of Different Brans on Loaf Volume of Brown Bread

Brown bread was produced by adding bran (all of the same nominal particle size range) from 10 widely differing wheat samples to a common base white flour. The different brans caused different levels of loaf volume depression. In all cases, dry heat-treatment of the brans decreased total reducing substances, inactivated lipase and increased loaf volume and height. However, the loaves still differed somewhat in volume. A similar study was conducted with three bran fractions of different sizes (Pollard <0.75 mm diam., Select >0.75 mm <1.8 mm and Digestive >1.8 mm), from the same grist, to a common base white flour. Smallest loaf volumes were obtained with Pollard and largest with Digestive. Subjecting the brans to the heattreatment, increased loaf volume. However, smallest volumes were still obtained with Pollard. Brans were also milled to a common maximum particle size (<0.7 mm) and then heat-treated. Reducing the particle size in general decreased loaf volume, but the heat-treatment counteracted the adverse effect of reduced particle size. It is concluded that bran exerts both a chemical effect (probably due to the lipid-metabolising enzymes and glutathione in the bran), and a physical effect (related to bran particle size and shape) on brown bread loaf size. The addition of either large bran particles, or heat-treated smaller bran particles to white base flour are potential methods of optimising brown bread loaf size.