Structural and physical characteristics of waxy and other wheat starches

Structures and properties of starches isolated from waxy wheat, amylose-reduced wheat (Kanto 107), and normal hard red winter wheat (Centura and a commercial product) grains were examined. Apparent amylose contents of the four starches were <0.2, 21.5, 26.2, and 26.6%, respectively. Waxy wheat amylopectin (AP) had the largest molecular weight (Mw) and no detectable extra-long branch-chains. The Mw of the AP displayed a negative correlation with the amylose content of the wheat starch, whereas the proportion of extra-long branch-chains of AP displayed a positive correlation with amylose content. Relationships between the Mw and gyration radius (Rz) suggested that the structure of waxy AP was more compact than that of other wheat APs. Branch chain-length distributions of AP analyzed by high-performance anion-exchange chromatography (HPAEC) showed that the peak chain-lengths of all the wheat starches were at DP12, and average chain-lengths varied between DP23.5 and 24.9. Centura AP had the highest proportion of long branch-chains (DP≥25). Onset gelatinization temperatures of waxy wheat, Kanto107, Centura, and commercial wheat starches were 55.7, 57.5, 55.6, and 54.9°C, respectively, and enthalpy changes were 13.6, 11.8, 10.7, and 10.6 J/g, respectively. Differences in pasting temperature and peak viscosity between waxy and normal wheat starches were substantially greater than the differences between maize starch counterparts.