Effect of pH on aqueous structure of maize starches analyzed by HPSEC-MALLS-RI system

Molecular conformation of maize starches (waxy, normal and high amylose) was examined at different pH values (5–10) using an aqueous medium-pressured size exclusion column chromatography (SEC) connected to multi-angle laser light scattering (MALLS) and refractive index (RI) detectors. The starch molecules were partially degraded at pH 5 and 10, resulting in lower values for molar size and radius of gyration than those in neutral condition. The specific volume data revealed that the structural changes under an alkaline condition such as pH 10 was more significant for amylose than that for amylopectin. Logarithmic ratios between molar size and radius of gyration were similar (0.2–0.3) for the amylopectins in waxy and normal maize starches, but higher (0.4–0.5) for the amylopectin in high amylose starch, indicating that the amylopectins in waxy or normal maize starches had sphere forms whereas that in high amylose starch had a random coil shape.