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Structural Properties of Starch Fractions Isolated from Normal and Mutant Corn Genotypes Using Different Methods

¹Department of Food Science and Human Nutrition and Center for Crops Utilization and Research, 2312 Food Sciences Building, Iowa State University, Ames, Iowa 50011. ²Department of Food Science, The Pennsylvania State University, 107A Borland Laboratory, University Park, PA 16802. ³BASF Plant Science, L.L.C., Ames Research, 2901 S. Loop Drive, Building 3, Suite 3800, Ames, IA 50010. ⁴Corresponding author. Phone: 515-294-9688. Fax: 515-294-8181. E-mail: pjwhite@iastate.edu

The objectives of this research study were to isolate, evaluate, and compare the fine structures of starch fractions obtained from a wild-type (normal) corn starch and amylose-extender25, dull39, sugary2, and sugary1 corn mutants in the same genetic background using three different fractionation procedures based on gel-permeation chromatography or alcohol-precipitation methods. Starch fractions obtained from each of the three methods were enzymatically debranched and analyzed using high-performance anion-exchange chromatography with a postcolumn amyloglucosidase reactor and a pulsed amperometric detector. The separations were performed by fractionation on a GPC column, by precipitation with 1-butanol, and by preferential precipitation with 1-butanol and isoamyl alcohol. Using any of these methods, no apparent differences in the molecular weight distributions of amylopectin or of amylose among the different starches were observed. The proportions of branch chain lengths of the starch components obtained by the various fractionation methods were very similar among methods for each of the starch types analyzed, such as the predominance of long branch chains in ae25 corn and that of the short branch chains in su2 corn. Overall, the effect of the corn mutations was more important to the differences observed among the starch types than was the method of fractionation used.