An improved colorimetric procedure for determining apparent and total amylose in cereal and other starches

An improved method for the colorimetric determination of amylose as its blue polyiodide complex is described. Starch is dissolved in urea—dimethylsulphoxide and aliquots of the solution are used to determine apparent amylose (measured in the presence of any amylose complexing monoacyl lipids which may be present) and total amylose (measured on lipid-free starch, precipitated from urea—dimethylsulphoxide solution with ethanol). When factors such as ionic concentration, sequence and timing of steps in the procedure and solution temperature are controlled, the coefficient of variation in replicate determinations (n = 6) is 0·2–10·0%, except with waxy starches, where it is 10·6–10·8%. The limitations of the method and sources of error in published methods for the preparation of lipid-free starches and in the development of stable amylose-polyiodide colour complexes are discussed. In some wheat and non-waxy rice starches the difference between total and apparent amylose is 30·5–7·4% amylose.