Cereal Chem 1990 | Macromolecular and Functional Properties of Native and Extrusion-Cooked Corn Starch.

Cereal Chem 67:490-499 | VIEW ARTICLE

Macromolecular and Functional Properties of Native and Extrusion-Cooked Corn Starch.

R. Chinnaswamy and M. A. Hanna. Copyright 1990 by the American Association of Cereal Chemists, Inc.

Normal corn starch (25% amylose) was extrusion cooked at different moisture contents (10-30%, db) and barrel temperatures (110-200 C). The expansion ratio was maximum for 14% moisture normal corn starch extrusion cooked at 150 C. The shear strength and slurry viscosity of the extrusion-cooked starches increased while the water solubility decreased with increasing starch moisture content. Gel permeation chromatography fractionation of the extrusion-cooked starches showed that the fraction I content (void volume peak) decreased with decreasing moisture content. Similar attribute pattern changes were seen with extrusion temperature. Corn starches with amylose contents from 0 to 70% were extrusion cooked at 150 C and 14% moisture content. Gel permeation chromatography fractionation showed that the fraction I content of the native starches decreased as the amylose content of the starch increased. Fraction II increased proportionately. Among the starches studied, the maximum expansion ration of 16.4 was obtained with 50% native amylose starch which had 2.75 mg of starch in fraction I per 5 mg of native starch fractionated. Upon extrusion cooking, the fraction I content decreased further. The changes in the contents of fraction I, however, showed that the branched starch component underwent degradation. The addition of sodium chloride, sodium bicarbonate, and urea further degraded fraction I. Sodium bicarbonate seemed to degrade the starch molecules to a greater extent than did the other chemicals. A new fraction III appeared between fractions I and II in some samples of native starches after addition of chemical agents. Fractionation of pure amylose and amylopectin before and after extrusion cooking indicated that the branched component, amylopectin, degraded to a greater extent than its linear counterpart, amylose.