The linear relationship between iodine staining and average chain length of the unbranched amyloglucans

Abstract

AbstractA simple straight‐line relationship between iodine staining and the average chain length (CL) of the linear amyloglucans has been derived utilizing the published data of Baldwin et al. [J. Am. Chem. Soc. 66, 111 (1944)], Bailey and Whelan [J. Biol. Chem. 236, 939 (1961)], Szejtli et al. [Biopolymers 5, 5 (1976)], Pfannemüller et al. [Biopolymers 10, 243 (1971)], and Banks et al. [Carbohydr. Res. 17, 25 (1971)]. The iodine staining characteristics—the wavelength of maximal optical absorbance (λM); the maximal absorbance (AM); and the iodine binding capacity (Ib) per chain—are all linearly related to the chain length. As an example, Ib per chain is linearly related to the CL and in the formula of a straight line: Y = nX − c where Y equals Ib per chain (or Ib × CL); X equals the CL, n is the slope, and c is the intercept of the Y‐axis by the straight line. Thus, CL and Ib are related as follows: CL = c/(n − Ib) Using the data of Banks et al., it was found that the slope was not affected by changes in temperature, but the Y‐intercept became less negative with decreasing temperature. Thus, the number of glucose residues per iodine molecule in the helix did not change, but shorter chain length species could complex with the iodine, and a larger fraction of each chain could form the helical configuration with iodine as the temperature was reduced. These findings suggest that the CL and therefore the number‐average degree of polymerization and the number‐average molecular weight of the unbranched amyloglucans could be determined by AM, Ib or λM measurements after standardization under precise experimental conditions.