Cereal Chem 67:551-557 | VIEW
Swelling and Gelatinization of Cereal Starches. I. Effects of Amylopectin, Amylose, and Lipids.
R. F. Tester and W. R. Morrison. Copyright 1990 by the American Association of Cereal Chemists, Inc.
A method was developed for measuring the volume of water absorbed by starch granules heated in excess water, based on the observation that blue dextran dye (molecular weight 2 x 10(6)) will dissolve in supernatant and interstitial water but not in the intragranular water. Swelling curves of wheat and normal and waxy barley and maize starches, determined by measuring the swelling factor (swollen volume/initial volume of air-dried starch) at various temperatures up to 85 C, were characterized by an initial stage of maximum swelling (not observed with high-gelatinizing starches or if granules disintegrated). With wheat starch, swelling began at 45-50 C and continued to 85 C; loss of birefringence and a large decrease in gelatinization enthalpy attributed to dissociation of crystalline clusters occurred at 50-55 C, and residual enthalpy attributed to dissociation of double helices was lost at 55-60 C with all starches, leaching of polysaccharide (amylose and/or amylopectin, depending on the starch) was highly correlated with swelling factor. Experiments with waxy and normal starches lead to the conclusion that swelling is a property of the amylopectin. In normal cereal starches, amylose and lipids actively inhibit swelling, except in barley starch above 60 C where they only act as diluents. Characteristic buckling of lenticular A-granules from wheat and barley (waxy and normal types) is attributed to preferential swelling and leaching of polysaccharide at the equatorial groove, where there is less amylose and lipid and where the amylopectin appears to be less crystalline.