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Thermal Properties of Starch in Corn Variants Isolated After Chemical Mutagenesis of Inbred Line B73¹

¹Journal Paper No. J-17696 of the Iowa Agriculture and Home Economics Experiment Station, Iowa State University, Ames, IA. Project nos. 3507 and 3134. ²Graduate student and professor, respectively, Department of Food Science and Human Nutrition, and Center for Crops Utilization Research, Iowa State University, 2312 Food Science Building, Ames, IA 50011. ³Professor, Department of Agronomy, Iowa State University. ⁴Research geneticist, USDA-ARS, Corn Insects and Crop Genetics Research Unit, Department of Agronomy, Iowa State University. ⁵Corresponding author. E-mail: pjwhite@iastate.edu Phone: 515/294-9688. Fax: 515/294-8181.

The starch from eight ethyl methanesulfonate (EMS) treated M4 families of the corn (Zea mays L.) inbred line B73 was analyzed using differential scanning calorimetry (DSC), a Rapid Visco Analyser (RVA), a texture analyzer (TA), and scanning electron microscopy (SEM) coupled with image analysis. The eight families were chosen from 144 families previously selected for having starch with unusual DSC parameters. Apparent amylose contents of the starch from the eight families generally were lower than that of the control. According to DSC, starches from mutagenized families tended to have lower onset temperature (T₀) of gelatinization, enthalpy (ΔH) of gelatinization, and peak height index (PHI), but broader gelatinization range (R) than the B73 control. Their values for ΔH and percentage of retrograzdation (%R) were clustered around that of the control. Pasting properties from the RVA of the starches from the M4 families also were clustered around those of the control B73 starch, except for the setback values which were lower than B73 for M4 starches. Gel firmness values, as measured by TA, of all the M4 starches were generally lower than that of the B73 starch at storage treatments of one day at 25°C or seven days at 4°C. The stickiness of the gels of the M4 starches tended to be greater than that of B73 after seven days of storage at 4°C. These observations were consistent with the lower apparent amylose values for the M4 starches. SEM and image analysis data revealed no differences among the treatments in granule size and shape. Possibly, EMS treatment altered the genes, affecting internal structure of the starch granules. Starch from the mutagenized families likely had lower bonding forces among molecules and fewer long chains in the amylopectin molecules than did B73.