Thermal properties of starch in corn variants isolated after chemical mutagenesis of inbred line B73

The starch from eight ethyl methanesulfonate (EMS) treated M4 families of t he corn (Zen mays L.) inbred line B73 was analyzed using differential scann ing 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 starc h from the eight families generally were lower than that of the control. Ac cording to DSC, starches from mutagenized families tended to have lower ons et temperature (T-0) of gelatinization, enthalpy (Delta H) of gelatinizatio n, and peak height index (PHI), but broader gelatinization range (R) than t he B73 control. Their values for Delta H 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 t han 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 tr eatments of one day at 25 degrees C or seven days at 4 degrees C. The stick iness of the gels of the M4 starches tended to be greater than that of B73 after seven days of storage at 4 degrees C. The:se observations were consis tent with the lower apparent amylose values for the M4 starches. SEM and im age analysis data revealed no differences among the treatments in granule s ize and shape. Possibly, EMS treatment: altered the genes, affecting intern al structure of the starch granules. Starch fi-om the mutagenized families likely had lower bonding forces among molecules and fewer long chains in th e amylopectin molecules than did B73.