Characterization of maize amylose-extender (ae) mutant starches. Part III: Structures and properties of the Naegeli dextrins

The objective of this study was to understand the crystalline structures of maize ae-mutant starches by analyzing the structures and properties of their Naegeli dextrins. After an exhaustive acid hydrolysis of the starch granules with sulfuric acid (15.3%, v/v) at 38 °C for up to 102 days, the maize ae-mutant starches produced 18.3–39.5% Naegeli dextrins. The Naegeli dextrins showed the B-type polymorph and displayed similar onset (45.1–51.4 °C), peak (113.9–122.2 °C), and conclusion (148.0–160.0 °C) gelatinization-temperatures and large enthalpy changes (21.8–31.3 J/g) and percentage crystallinity (77.0–79.2%). The Naegeli dextrins showed unimodal molecular-size distributions with the peak molecular-size at degree of polymerization (DP) 16. The molecular-size distributions of the Naegeli dextrins did not significantly change after debranching with isoamylase, indicating predominantly linear molecules. The isoamylase-treated Naegeli dextrins had average chain lengths of DP 23.8–27.5 and large proportions of long chains (DP ≥ 25, 36.7–52.7%), resulting from hydrolysis of amylose double helices.