| Starch is a renewable biomaterial with increasing uses in food, fuel, chemicals, plastics, textiles, paper, and building materials. The principal source of starch is the cereal grains, especially corn. Grain sorghum is consumed almost exclusively in animal feed in the USA, but in the future it is likely to be used to produce starch and other value-added products.; A small-scale (100g of grain) procedure, developed to suit a breeding program, was devised to wet-mill grain sorghum into six fractions. The wet-milling process was replicated five times on commercial grain sorghum, and the mean yield (69.4%) of starch (≤0.3% protein) varied by 0.3%, whereas the yields of fiber, gluten, and germ plus bran fractions varied by 5–6%. The starch fraction accounted for ∼95% of that in the grain, while the total solids recovered was 99.0%. Four other samples of grain sorghum gave 92–95% recoveries of starches and 98.2–99.8% total solids recovery. All grain sorghum starches had lightness (L*) values and pasting curves nearly equal to those of a commercial corn starch.; To encourage wet-milling of current hybrids of grain sorghum, an abbreviated wet-milling process was developed that gave two products; starch, obtained in over 78% recovery, and an animal feed, which comprised the remaining solids. In a model study steep time (1–3h), steep temperature (25–60°C), and coarse-grinding speed (tip speed of blade 90.4–150.7 Km/h) were varied, and starch recovery, starch lightness (L*), and damaged starch were measured. In the surface-response study, recovery of starch ranged from 57 to 89%, starch protein content from 0.4 to 0.5%, and lightness (L*) from 90 to 93. Damaged starch content was constant at around 0.4%. Commercial grain sorghum gave the highest starch recovery (90%) after steeping 2h at 55°C and a coarse-grinding of speed 124.6 Km/h, whereas a food-grade, a white and a red sorghum gave 85, 84, and 80% recoveries, respectively. The four starches had lightness (L*) 93–94 and damaged starch 0.4–0.6%. When the commercial grain sorghum was wet-ground at 124.6 Km/h without steeping in 2 parts of water containing 0.2% sulfur dioxide, a 78% recovery of starch was obtained with L* 93.7 and starch damage 0.5%. |
