Isolation and characterisation of high‐molecular‐weight amylose by dispersion of starch granules with urea

Starch granules (defatted and hydrated) are completely dissolved by prolonged contact with urea under extremely mild conditions (10M, pH 6,2 at 26–28°C). The microscopic examination has revealed that the granules undergo a considerable swelling in contact with the urea, followed by a progressive leaching of the starch components, with a simultaneous loss in birefringence, increase in viscosity and clarity of the solution leading to the complete dissolution of the granules. The dispersion profiles display a biphasic pattern and appear to be characteristic of the source. Amylose is isolated from the solution by different procedures. Trace quantities of amylose from amylopectin +ction are removed by adsorption on defatted cellulose. The purified products are recovered by precipitation with ethanol and washed free of urea with ethanol. The amylose and the amylopectin are characterized by determining their iodine binding capacity (IBC), blue value (BV), intrinsic viscosity ([η]), and beta‐amylosis limit. The method is suitable for the isolation of high molecular weight amylose and amylopectin from cereal and tuber starches on a preparative scale.