OPTIMIZATION OF SULFUR-DIOXIDE AND LACTIC-ACID STEEPING CONCENTRATIONS FOR WET-MILLING OF GRAIN-SORGHUM

Influence of sulfur dioxide (SO2) and lactic acid (LA) on grain sorghu m steeping efficiency in terms of wet-milling characteristics was inve stigated using response surface analysis. Tested ranges of concentrati ons in steeping water were 0.050 to 0.278% and 0 to 0.282% for SO2 and LA, respectively Measured wet-milling variables were steeping solids yield, starch yield, protein yield, fiber/germ yield, starch recovery, protein recovery and protein content of starch. Starch and protein re covery values were highly correlated to each other (r = 0.74). Correla tions of these attributes with fiber/germ yield were strongly negative (r = -0.96 and r = -0.70 for starch and protein recover): respectivel y). A model comprised of the linear and quadratic terms of SO2 and LA concentrations and the interaction between SO2 and LA was fitted to da ta for each dependent variable. The model satisfactorily explained sta rch yield (R-2 = 0.84), starch recovery (R-2 = 0.65) and fiber/germ yi eld (R-2 = 0.71). Lactic acid was the factor that consistently influen ced all significant surfaces (P < 0.01 for starch yield and starch rec overy, and P < 0.05 for fiber/germ yield). Maximum stationary points f or starch yield and recovery, and a minimum stationary point for fiber /germ yield were observed at similar combinations of SO2 (0.191-0.209% ) and LA (1.387-1.415%) concentrations.