Structure, thermal stability and suspension rheological properties of alcohol-alkali-treated waxy rice starch

Abstract

In this work, the effect of alcoholic-alkaline treatment on the characteristics of waxy rice starch (WRS) and its aqueous suspensions was studied for the first time. Microscopy shows that the alcohol-alkali-treated WRS (AAT-WRS) was in the form of particles of lengths between 10 and 50 μm. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses indicate that the original A-type crystallites of WRS had been completely eliminated by the alcoholic-alkaline treatment and no new crystalline structure was formed. Fourier-transform infrared (FTIR) spectroscopy confirms the absence of chemical reactions during the treatment. Thermogravimetric analysis (TGA) results indicated the decreased thermal stability of AAT-WRS, which may be attributed to the amorphous structure and possible degradation resulting from the treatment. Compared with the gelatinized starch suspension, the AAT-WRS aqueous suspension presented a weaker shear-thinning behaviour, lower steady-shear viscosity, lower storage and loss moduli, and higher loss tangent, which suggest a less-rigid gel structure. The rigidity of the gel further decreased with higher temperatures. Our results here could provide insights into the rational design of modified starch products with waxy rice starch.

Keywords: Alcoholic-alkaline treatment; Crystallinity; Morphology; Rheological properties; Thermal stability; Waxy rice starch.