Macromolecular features of amaranth starch

High-performance size-exclusion chromatography (HPSEC), static light scattering (SLS) and dynamic light scattering (DLS) techniques were used for the structural characterization of amaranth starch, solubilized in water by microwave heating in a high-pressure vessel. Apparent average molar mass (M(w)) gyration radius (R(G)), and hydrodynamic radius (R(H)) values were obtained from Berry and Zimm treatment of light-scattering data. When heating time increased from 35 to 90 sec, the M(w), R(G), and R(H) decreased, demonstrating a possible polymer degradation due to temperature. Apparent M(r) values from HPSEC at 35 sec (27 ± 2 x 10⁷ g/mol) and 50 sec (20 ± 2 x 10⁷ g/mol) were lower than those determined by SLS (35 sec = 69 x 10⁷ g/mol, 50 sec = 56 x 10⁷ g/mol). However, at 70 and 90 sec, the inverse pattern was obtained. The fractal dimensions (d(f)') from HPSEC study for samples dissolved for 35 (3.26), 50 (3.24), and 70 sec (3.14) are characteristic of a particle that has the internal structure of hard sphere, and for samples dissolved for 90 sec (2.19), are characteristic of a fully swollen, randomly branched macromolecule. From SLS, d(f)' decreased with increasing treatment time (d(f)' = 2.44, 2.18, 1.50, and 1.03 for 35, 50, 70, and 90 sec, respectively). The particle-scattering factors and Kratky plots, well-suited for studying the internal structure of a macromolecule, showed a sample degradation when treatment time increased. Results from DLS showed bimodal distributions with differences in the peak locations when treatment time increased. The ratio of R(G) to R(H) (ρ) for samples analyzed were between 0.88 and 1.3; these values are characteristic of a sphere or globular structure.