Preparation and physicochemical properties of three types of modified glutinous rice starches

Hydroxypropylated, phosphorylated, and hydroxypropyl-phosphorylated starches were prepared from glutinous rice starch, and their physicochemical and structural properties were investigated. With increasing reaction time, the molar or degree of substitution of modified starches increased. SEM micrographs revealed that phosphorylated starch granules retained their relative integrity, while some cracks appeared on the surface of hydroxypropylated and hydroxypropyl-phosphorylated starch granules. RVA analyses revealed that pasting properties improved after chemical modification. Additionally, chemical modification improved freeze-thaw stability, especially in hydroxypropyl-phosphorylated starch. DSC analyses showed that onset temperature and gelatinization enthalpy decreased with increasing reaction time, especially in the dual-modified starch. X-ray diffraction patterns revealed that native and modified starches had A-type crystalline patterns. FT-IR spectra showed some minor spectral differences after modification. (13)C CP/MAS NMR spectra showed that a novel peak appeared at 20 ppm after hydroxypropylation and that the relative intensity signals in the C4 region increased after phosphorylation.