Cereal Chem 64:154-157   |  VIEW ARTICLE

Stearic Acid-Starch Interactions as Measured by Electron Spin Resonance.

L. E. Pearce, E. A. Davis, J. Gordon, and W. G. Miller. Copyright 1987 by the American Association of Cereal Chemists, Inc. 

The binding of stearic acid to molecules of starch was explored by using spin probes and electron spin resonance spectroscopy at room temperature, elevated temperatures, and after heating and cooling with wheat, corn, high-amylose, and waxy corn starches. The effect of the location of the spin probe along the fatty acid chain was determined using two spin probes, 16-DOXYL and 5-DOXYL-stearic acid. Methyl 5- DOXYL-stearate was used to determine the effect of replacing the carboxyl group on stearic acid with a methyl ester. Crystallinity patterns for each starch type were verified by wide-angle X-ray diffraction. Immobilization of stearic acid spin probes occurred for all starch types at room temperature before and after heating and cooling. The extent of stearic acid spin probe immobilization was not different in amylose- containing starches at room temperature or heated and cooled samples. However, the immobilization of stearic acid spin probes was less in waxy corn starch than in the amylose-containing starches at room temperature before heating,and the immobilization became even less in waxy corn starch after heating and cooling. Electron spin resonance spectra at elevated temperatures showed stearic acid spin probes were released during heating, but starch-stearic acid interactions again occurred during cooling to room temperature. Spectra for systems of 5-DOXYL-stearic acid and starch or methyl 5-DOXYL-stearate and starch showed probe binding to be with the hydrocarbon end of stearic acid rather than the carboxyl end. Wide-angle X-ray diffraction patterns were more crystalline as the amylose content of starch was reduced and were typical of each starch type.