Cereal Chem. 70:81-89   |  VIEW ARTICLE

Fine Structure of Amylopectin in Relation to Gelatinization and Retrogradation Behavior of Maize Starches from Three wx-Containing Genotypes in Two Inbred Lines.

R. C. Yuan, D. B. Thompson, and C. D. Boyer. Copyright 1993 by the American Association of Cereal Chemists, Inc. 

Maize starches from three wx-containing genotypes (wx, du wx, and ae wx) in two inbred lines (W64A and Ia5125) were examined to evaluate the effect of mutant genotype on amylopectin fine structure and thermal behavior of starch granules. The amylopectin chain length distribution and A:B chain ratio were investigated by enzymatic treatments followed by high-performance size-exclusion chromatographic separation. Gelatinization and retrogradation behavior at 10 and 30% starch concentrations were studied by differential scanning calorimetry. Chain length distribution profiles of the isoamylase-debranched amylopectins showed distinct patterns according to genotypes. Starch from the ae wx genotype in both lines had a greater proportion of longer chains (degree of polymerization greater than 30) than the other genotypes. The A:B chain ratios were calculated from the high-performance size-exclusion chromatograms of the debranched beta-limit dextrins. Except starch from the ae wx genotype of the W64A line, which had an A:B chain ratio of 1.5, all of the samples had A:B chain ratios within the range of 0.9-1.1. The A:B chain ratio of 1.5, together with the high proportion of longer chains in that sample, is consistent with the interpretation that the population of A chains in this sample contains some unusually long chains. In both lines, the starch granules from the ae wx genotype had the highest DeltaH and Tmax for both gelatinization and retrogradation. The high DeltaH for the ae wx starches might be attributed to greater amounts of longer chains in these amylopectins. Except the starches from the wx genotype at 10% concentration, all of the gelatinized starch samples showed a differential scanning calorimetry endothermic peak after being stored at 4 C for seven days. Retrogradation DeltaH was highest for the ae wx starches, both in absolute terms and as the proportion of gelatinization DeltaH. In most cases retrogradation DeltaH was higher (on dry weight basis) for 30% than for 10% starch; for the du wx starches, the DeltaH at 30% starch was approximately twice that at 10%.