Extraction of Wheat Starch with Aqueous Sodium Hydroxide

Abstract

ABSTRACTWheat starch was extracted with aqueous sodium hydroxide at 30–38% starch solids, pH 11.5–12.3, and 25–42°C for 0.17–24 hr. Stirring wheat starch at pH 12.3 and 25°C for 3 and 24 hr, then washing with water, neutralizing, and washing again, removed 70 and 90% phosphorus (P), respectively. Adding 16% sodium sulfate (dry starch basis) into the alkaline medium removed ≈80% of P at pH 12.0 and 25°C in 3 hr and >95% of P at pH 11.7 and 42°C in 3 hr. Sulfate ion was absorbed strongly by wheat starch in aqueous sodium hydroxide at pH 12.0, and sodium sulfate also increased the starch's uptake of hydroxide ion. Low‐P wheat starch (>90% of P removed) retained the fatty acids in the untreated starch, but a fatty acid‐amylose complex was not detectable by differential scanning colorimetry. The enthalpy of gelatinization of the low‐P wheat starch almost matched that of prime starch, as did its X‐ray diffraction pattern. Those data are consistent with saponification of the lysophospholipid in the amorphous phase of the starch to form fatty acid salts and glycerol‐choline or glycerol‐ethanolamine phosphodiesters that slowly diffused out of the granules. The low‐P wheat starch was judged to have less “cereal” odor than the prime starch, and its pasting temperature at 9.3% starch solids was lowered by ≈10°C.