| A bench-scale wet-milling test for wheat flour was devised to mimic the industrial processes that begin with a highly sheared flour-water dispersion (HS-FWD). The test was developed on a Regional Baking Standard (RBS-98) flour, which is a flour of 76 hard winter wheat composites. The HS-FWD wet-milling test included: (i) high-shear mixing of the flour (65.0 g, db) and water (100 mL, 35°C) with a homogenizer to form a HS-FWD; (ii) centrifugal fractionation (2,500 x g/15 min) of the HS-FWD into supernatant, protein-rich, and starch phases; (iii) aging of the protein-rich phase; and (iv) isolation and purification of five fractions (the gluten, A-starch, B-starch, fiber, and water-solubles). Response surface methodology was used to optimize the high-shear mixing and gluten-aging steps. Regression models showed that water-flour (db) ratios of 1.6–1.8, homogenizer speeds of 5,000–7,000 rpm, and added-water temperature of 30–35°C in the high-shear mixing step gave high recoveries (80–84%) of the A-starch fraction with 0.20–0.30% protein. The highest recovery (∼78%) of flour protein in the gluten fraction with ∼83% (db) protein (Nx5.7) was achieved when the protein-rich phase was aged in added water (100 mL) at 30–40°C for 15–25 min without agitation. At the optimal process conditions (water-flour ratio: 1.7, homogenizer speed: 6,000 rpm, water temperature: 35°C, gluten aging temperature and time: 40°C and 20 min, the Glutomatic washing time of the aged gluten: 2.0 min), 80.3% of flour starch was recovered in the A-starch fraction with 0.24% protein, 78.8% of flour protein in the gluten fraction with 82.9% protein, and 98.8% of flour solids in the five wet-milling fractions. The recoveries of starch and protein by the HS-FWD wet-milling test were 7–10% lower as compared to the Martin dough-washing method. The Rapid Visco-Analyzer (RVA) pasting curves of the A-starch fractions and the breadmaking qualities of the gluten fractions isolated by the two tests were comparable. Flours with weak compared to strong dough-mixing characteristics, including flours of hard wheats, a soft wheat, and waxy wheats, generally gave lower recoveries of the A-starch fractions with 0.20–0.30% protein. The missing A-starch either contaminated the gluten fraction and lowered its protein content, or increased the B-starch fraction. |
