Effect of sorghum flour composition and particle size on quality properties of gluten-free bread

White, food-grade sorghum was milled to flour of varying extraction rates (60%, 80%, and 100%) and pin-milled at different speeds (no pin-milling, low-speed, and high-speed) to create flours of both variable composition and particle size. Flours were characterized for flour composition, total starch content, particle size distribution, color, damaged starch, and water absorption. Bread was characterized for specific volume, crumb structure properties, and crumb firmness. Significant differences were found (P < 0.05) in the composition of sorghum flours of varying extraction rate, most notably for fiber and total starch contents. Flour particle size and starch damage were significantly impacted by extraction rate and speed of pin-milling. Water absorption increased significantly with increasing extraction rate and pin-milling speed. Breads produced from 60% extraction flour had significantly higher specific volumes, better crumb properties, and lower crumb firmness when compared with all other extractions and flour types. The specific volume of bread slices ranged from 2.01 mL/g (100% extraction, no pin-milling) to 2.54 mL/g (60% extraction, low-speed pin-milling), whereas the firmness ranged from 553.28 g (60% extraction, high-speed pin-milling) to 1096.26 g (commercial flour, no pin-milling). The bread characteristics were significantly impacted by flour properties, specifically particle size, starch damage, and fiber content (P < 0.05).