Iodine binding capacity

To determine the amylose content of starch, the iodine reaction has been most commonly used because amylose and amylopectin have different abilities to bind iodine. The methods such as blue value (absorbance at 680 nm for starch-iodine complex using amylose and amylopectin standards), and potentiometric and amperometric titration have been used for more than 50 years. These procedures are based on the capacity of amylose to form helical inclusion complexes with iodine, which display a blue color characterized by a maximum absorption wavelength (kmax) above 620 nm. During the titration of starch with iodine solution, the amount (mg) of iodine bound to 100 mg of starch is determined. The value is defined as iodine-binding capacity or iodine affinity (lA). The amylose content is based on the iodine affinity of starch vs. purified linear fraction from the standard 100 mg pure linear amylose fraction has an iodine affinity of 19.5-21.0mg depending on amylose source. Amylopectin binds 0-1.2mg iodine per 100mg (Banks and Greenwood, 1975). The amylose content determined by potentiometric titration is considered an absolute amylose content if the sample is defatted before analysis. 

Amylose, although water soluble, gives an unstable solution which irreversibly precipitates. It is mainly responsible for the deep blue coloration given by starch and iodine. Solutions of amylopectin are relatively stable. The iodine-binding capacity, on the other hand, is very low. A small amount of covalently bound phosphate normally appears with starch but its exact location within the molecule is not known. 

Fig. 12.—The iodine-binding capacity (IBC) of starch (in %) as a function of the concentration of free molecular iodine (in mol). (Reprinted with permission from J. Hollo and J. Szejtli, Brauwissenschaft, 13 (1960) 348-352.)...

The amount of iodine complexed by starch of various origins depends on the same factors as the NMR spectra. There are satisfactory linear correlations between the iodine-binding capacity and the percentage of terminal glucose units of starch. The latter could be calculated from the intensities of the proton and carbon chemical shifts.81... 

Properties of Complexed Amylose and Amylopectin 7 Iodine-Binding Capacity... 

The iodine-binding capacity of starch is dependent on the degree of polymerization (DP). Amylose forms with iodine a helical inclusion complex with an intense blue colour, which possesses an absorption maximum at wavelengths between 620 and 680 nm. Amylopectin has much less iodine-binding capacity because of its branched character, leading to a red-violet colour with absorption maximum of 540 nm 31. 

Kim and Robinson have shown that the helical conformation of amylose was the most important factor in the binding of surfactant molecules in the helical cavity of amylose chain, resulting in a slight decrease in the intrinsic viscosity, fall in the p-amylolysis limit and the iodine binding capacity(29)... 

Iodine Binding Capacity (ISO) Blue Value (BV) 6-amylolysis Limit( ) Intrinsic viscosity 10-2.ft )/ cm- g- ... 

A spectrophotometric method is developed for the determination of iodine binding capacity for starch and Its components on. a micro-scale. The absorption spectra of Iodine In aqueous solution In acetate buffer pH 4,8, exhibits three distinct peaks at 286,... 

Iodine Binding Capacity (IBC) of Potato Starch and Its Components... 

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