Cereal Chem 66:228-232   |  VIEW ARTICLE

Differential Water Solubility of Corn and Sorghum Starches as Characterized by High- Performance Size-Exclusion Chromatography.

D. S. Jackson, R. D. Waniska, and L. W. Rooney. Copyright 1989 by the American Association of Cereal Chemists, Inc. 

The inherent water solubility properties of corn and sorghum starches were studied with high-performance size-exclusion chromatography (HPSEC). Corn starches containing less than 1, 25, 53, and 70% amylose (AMY), and sorghum starches containing less than 1, 17, 23, and 24% AMY were solubilized in water. Corn starch was solubilized at 85 C for 1 or 4 hr by traditional aqueous leaching procedures. Corn and sorghum starches were also solubilized at 65 C, 85 C, or boiled and autoclaved, and subsequently sonicated. After treatment, starch solutions were centrifuged and filtered in preparation for HPSEC analysis. Traditional aqueous leaching solubilized mostly AMY. Soluble AMY had a smaller hydrodynamic volume and hence a smaller apparent molecular weight as the starches increased in total AMY content. AMY was more soluble on a percentage basis from starch with less total AMY than from starch containing more AMY. Starch treated at different temperatures had an increased amount of starch solubilized and an increased apparent molecular weight of AMY at higher temperatures. Differential scanning calorimetry endotherms showed that crystalline regions from high AMY starch were not melted at 85 C, and as a result, these starches had lower HPSEC water solubilities. The endotherms showed that all sorghum starches melted below 85 C, yet AMY from sorghum starch with more total AMY was still less soluble. Hence, water solubility of AMY is governed by the crystalline melting behavior and total AMY content of the starch. Sorghum amylopectin (AMP), solubilized at 85 C, was separated into two populations. The AMP in cooked sorghum starches (120 C) was less soluble as the total sorghum AMP content increased. HPSEC AMP peaks from waxy starches show "tailing" in an area normally occupied by AMY molecules. HPSEC is a useful technique for characterizing the water-soluble components of native starch and starch-containing foods.