Abstract
AbstractThe Ewers method for the measurement of starch is currently the official EEC method for the measurement of starch purity. In this communication a critical assessment of variables affecting the Ewers method has been undertaken. It was found that the degree of hydrolytic degradation which occurs during the solubilisation of starch prior to polarimetric measurements is of crucial importance in the starch purity values obtained. Factors which influence the degree of hydrolytic degradation include hydrochloric acid concentration to a large extent, and heating and cooling times to a lesser extent. It has been shown also that the clarifing reagent of Carrez, which is used in Ewers method for the removal of other chiral molecules such as protein, etc, adsorbs lower molecular weight malto‐oligosaccharides leading to reduced starch purity values. For a series of starches with varying amylose: amylopectin ratios it was found that high amylopectin starches performed much better in Ewers method than high amylose starches. It is concluded that Ewers is not an acceptable satisfactory method for starch measurement on which to base quality control or eligibility for rebate and refund schemes.
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