POLARIMETRIC DETERMINATION OF STARCH IN CEREAL PRODUCTS: II. FACTORS AFFECTING THE SPECIFIC ROTATORY POWER OF WHEAT STARCH IN AQUEOUS CALCIUM CHLORIDE SOLUTIONS

Abstract

The addition of small amounts of 0.8% acetic acid to concentrated calcium chloride solutions is shown to cause a remarkable increase in the hydrogen ion concentration, the salt solution ordinarily being rendered more acid than the "acidifying" reagent. With 15 minutes' boiling at constant temperature and salt concentration the effect of pH on the specific rotatory power of wheat starch is negligible over the range 2.1 to 3.0. Above a pH of 4.0, the starch solutions are opalescent, filter slowly and revert to a gel upon standing, while at pH values below 2.0 the specific rotation value is depressed. Only a very small decrease in the specific rotation value results from extending the boiling period to one hour when the initial pH is between 2.5 and 2.2. The specific rotation value is depressed by rising extraction temperature to an extent that varies with the pH and extraction time. It is increased quite remarkably by rising salt concentration. On substituting magnesium chloride for calcium chloride, the specific rotation value for wheat starch is increased by approximately 7°. Starch concentration has negligible effects on the specific rotation value. The specific rotation value decreases with rising polarization temperature over the range 20° to 35 °C. Sorption of water by the filter paper causes a large increase in the polarization value for the first portions of filtrate, this effect varying with the kind and amount of filter paper that is employed.