SPECTROPHOTOMETRIC TITRATION OF STARCH POLYSACCHARIDES WITH IODINE

Two methods of spectrophotometric titration (SPT) are described. Method A describes the determination of the extinction (E) at 4 wavelengths (WL) 714, 625, 555, and 500 nm and of 16 concentrations of iodine in the range of [I] = 2.5 and 166.7 10(-5) N I-2 or pI = 4.60 and 2.28 (pI = -log [I]) as well as the calculation of the extinction-relationship R of two WL for 6 possible pair combinations. The dependence of E respectively of log [I] in form of E- or R-curves of amyloses, amylopectins, Nageli-amylodextrin and starches of several botanical sources are discussed under the aspect of the reaction of helical segments of molecules with iodine. Method B of the SPT defines E of the 4 wavelengths at pI 3.6 and 3.0 and calculation of the extinction relation ships R(M) and R(H) of middle (M) and high (H) concentrations of iodine. The position of the parameters R(M) and D = R(M) R(H) of the 6 wavelength combinations in each X-Y-diagram depends on the botanical origin of potato, tapioca, wheat and regular maize starch.