WET-MILLING CHARACTERISTICS OF PROPIONATE-TREATED HIGH-MOISTURE MAIZE .2. QUALITIES OF STARCH AND GLUTEN

High-moisture (25.6%) maize was treated with three forms of 1.0% propionate (weight treatments adjusted to obtain equivalent moles of propionate ion). These were propionic acid (99% pure, pH 1.7), a mixture of sodium propionate and sodium acetate acidified with HCI to the pKa of propionic acid (pH 4.8), and the same mixture of sodium propionate and sodium acetate acidified to the natural pH of propionic acid (pH 1.7). Another sample of the maize was forced-air dried (25-degrees-C) to 12% moisture content. Propionate-treated and untreated maize samples were stored at 25-degrees-C for six months before wet milling. Starch recovered from propionate-treated maize contained greater amounts of residual protein than did starch from untreated air-dried maize and was more yellow in color. Starch from propionate-treated maize had lower pasting viscosities than did starch from untreated air-dried maize, indicating partial hydrolysis. No differences in the thermal properties of the starches were observed. Gluten from propionate-treated maize contained lower concentrations of protein and was less yellow than gluten from untreated air-dried maize. Addition of a small amount of sodium chloride to the mill-starch slurry improved starch-gluten separation in propionate-treated maize.