Estimation of the Iodine Affinity of Starch by Three Types of the Automatic Titration

Abstract

Iodine affinity (I. A.) values of potato of starch (P. S.) and corn starch (C. S.) were estimated by three different types of the automatic titration and the results were compared with each other. (1) The apparatus reported previously of the automatic amperometric titration for I. A. estimation was partly improved. (2) The shape of the amperometric titration curve of P. S. was found to be different from that of C. S.. The difference might be due to a structural difference of amylopectin components of these starches. (3) The potentiometric titration for I. A. estimation was also carried out automatically. The same I. A. value (3.6) was obtained by the two titration methode for P. S., but for C. S. the value obtained by the potentiometric method (4.6) was slightly higher than the one by the amperometric method (4.3). (4) The sample of C. S. used contained an unidentified substance which affected considerably the potential value of the initial reaction mixture. (5) The I. A. value of starch was also calculated from the curves of the automatic photometric titration. The values obtained were widely varied with titration conditions; they were always higher than those estimated by the above two methods, and became higher as the concentration of starch decreased.