Effect of selected organic and inorganic acids on corn wet-milling yields

The use of alternative organic and inorganic acid (phosphoric acid, acetic acid, citric acid, sulfuric acid, and hydrogen chloride) to replace lactic acid in corn wet-milling steeping was studied. All acids were added into steepwater at a level of 0.55% (v/v) along with 0.2% (w/v) sulfur dioxide, steeped for 24 hr, and laboratory wet-milled to measure product yields and milling characteristics. All organic and inorganic acids added in the steep solution improved the yield of starch by an average of 4.36 percentage points over that of sulfur dioxide alone, with the increased starch coming primarily from the fiber fraction. The yield of starch was highly correlated to the difference of final and initial pH of the steepwater with a correlation coefficient of 0.9174 (P < 0.0001). Milling characteristics including gluten filtration time, germ skimming time, and percent of fiber in germ were improved by the addition of the acids. There was no practical difference in starch protein content due to the use of different acids. Acids other than lactic acid could be added into steeping systems where lactic acid fermentation does not occur to enhance the action of sulfur dioxide, to improve the yield of starch, and to facilitate separation of starch and protein.