Relationships between Functional Attributes and Molecular Structures of Amylose and Amylopectin Fractions from Corn Starch

Understanding starch structure−function relationships is vital to the continued development for new uses for starch. Fractionated corn amylose and amylopectin, with known molecular weights, chain lengths, and branching and crystalline ratios, were studied for pasting, gel textural, and retrogradation properties by rapid viscoanalysis, textural profile analysis, and differential scanning calorimetry. Amylose fractions with weight-average molecular weights ( M w ) of 2.47−1.36E+05 had chain number-average degrees of polymerization (DP n ) of 500−1000, 0−1 branch points per 1000 glucose units, higher setbacks, and high final viscosities and resulted in firmer gels than their lower M w counterparts. Cohesiveness was inversely proportional to crystallinity, while stringiness increased with increasing DP n . Amylopectin fractions of low M w (7.89−7.08E+07) with high branching ratios (>1.5), short branch chains (weight-average degree of polymerization, 15−18), and crystallinity >28% had high peak temperatures and low peak viscosity and shear thinned less. When cooled, these amylopectins formed weak gels, but during storage, the gels firmed and retrograded more than did their high M w counterparts.