Structure of fine waxy rice starch prepared via a compressed hot water process

Abstract

The structure of fine starch prepared via a compressed hot water process at different temperatures (160- 180 °C) was analyzed using dynamic light scattering and size-exclusion chromatography with multi-angle light scattering and differential refractive index detection. Changes in the molecular weight, polydispersity, hydrodynamic radius, and radius of gyration were assessed. The intrinsic viscosity of the fine starch solution was derived from the Flory-Fox and Ptitsyn-Eizner equations. The weight-averaged molecular weight decreased to 7.29×105 g/mol, and the average hydrodynamic radius and weight-averaged radius of gyration decreased by 34.9 nm and 14.6 nm, respectively, at 180 °C. In fine starch prepared at 160 °C, 165 °C, and 170 °C, tails in the multi-angle light scattering peaks, upswings in the conformation plots, and upturns in the plots of gyration radii and elution volumes were all the result of branching structures. At 175 °C and 180 °C, amylopectin branching was diminished and symmetric scattering peaks were observed. We propose a pathway for waxy rice starch hydrolysis by a compressed hot water process.