Starch granule-associated proteins affect the physicochemical properties of rice starch

The objective of this study was to investigate the effect of starch granule-associated proteins on the physicochemical properties of waxy, low-amylose rice and high-amylose rice starch. Starch granule-channel proteins (GCP) and total starch granule-associated proteins (tSGAP) were selectively removed. Extraction of GCP was responsible for increases in amylose leaching, swelling power and solubility, and caused drops in apparent crystallinity, final viscosity, gelatinization temperature, storage modulus, loss modulus and complex viscosity. Meanwhile, the removal of tSGAP led to an increase in solubility, peak viscosity and breakdown and decrease in apparent crystallinity, final viscosity, setback, gelatinization temperature, storage modulus and complex viscosity. Protein removal had no significant effect on the gelatinization enthalpy, double helix structure and hydrogen bond strength of amylopectin. Overall, GCP had a more substantial role in physicochemical changes than did starch surface proteins. GCP, tSGAP and the amylose/amylopectin ratio all contributed to the physicochemical properties of rice starch.