Iodine, complex with amylose

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. 

Figure 16-6 (a) Schematic structure of the starch-iodine complex. The amylose chain forms a helix around l6 units. [Adapted from A T. Calabrese and A. Khan, "Amylose-lodine Complex Formation with Kl Evidence for Absence of Iodide Ions Within the Complex." J. Polymer Sci. 1999, A37,2711.] (fc>) View down the starch helix. Showing iodine inside the helix.8 [Figure kindly provided by R. D. Hancock, [rower Engineering, Sett Lake City.]... 

The helical structure of amylose also serves as the basis for an interesting and useful reaction. The inside of the helix is just the right size and polarity to accept an iodine (I2) molecule. When iodine is lodged within this helix, a deep blue starch-iodine complex results (Figure 23-19). This is the basis of the starch-iodide test for oxidizers. The material to be tested is added to an aqueous solution of amylose and potassium iodide. If the material is an oxidizer, some of the iodide (I-) is oxidized to iodine (I2), which forms the blue complex with amylose. 

The starch-iodine complex of amylose. The amylose helix forms a blue charge-transfer complex with molecular iodine. 

Thus the blue inclusion complex becomes visible only when all the hydrogen sulfite has been consumed. According to studies by / . C. Teitelbaum, S. L. Ruby and T. ]. Marks the blue inclusion compound consists of the amylose component of the starch and the polyhalogenide anion Is", this was established by comparing the Raman and I Mofibauer spectra of the blue-black amylose-iodine complex with those of the adduct between trimesic acid hydrate and H Is , the structure of which is known (see figures). 

The iodine affinity is due to the formation of colored complexes with amylose. The color of this complex depends on both the concentration of the iodine in the solution and the kind of starch. Amylose binds 20% (v/v) of iodine, to develop a blue color, whereas amylopectin binds only O.S to 1% (v/v) of iodine to give a red-violet eolor. Starch which does not contain any amylose gives a red color with iodine. Thus, evaluation of the degree of dextrinization based on the observations of Komm and Martin needs standardization of the method and approach, because ofthe variability in the origin of the starch. Table XVI shows that methods in use to date are not equivalent to one another. The color-development characteristics are again dependent on the origin of the starch. ... 

Two methods were used one is the iodine method that was used to determine dextrinization or the ratio of hydrolysis of the starch, and the other is the phenolphifaalein method lhat was used to determine CD formation. Starch-dextrinizing activity was determined in accordance with Fuwa (19) and Pongasawasdi and Yagisawa (20) with slight modifications. The reaction mixture containing 100 (iL of diluted enzyme aliquot and 300 pL of 0.5% soluble starch prepared in 0.1 M acetate buffer, pH 5.5, was incubated at 55 °C for 10 min. The enzyme reaction was stopped by the addition of 4.0 mL of 0.2 M HCl solution. Then, 0.5 mL of iodine solution (0.3 g/L I2 and 3.0 g/L KI) was added to form an amylose-iodine complex with residual amylose. The final volume was adjusted to 10 mL with distilled water. The absorbance of the blue color of the amylose-iodine complex was measured by spectrophotometer at 700 nm, and a decrease in absorbance was verified, when compared to a control tube with heat-inactivated enzyme. One unit of enzyme activity was defined as the quantity of enzyme that reduces the blue color of the starch-iodine complex by 10% per minute. 

The Interaction of Sodium Dodecyl Sulfate, a Competing Ligand, with Iodine Complexes of Amylose and Amylopectin... 

We have reported a novel reversible interaction of amylose-iodine-complex with proteins, which is closely associated with the coil— helix transition of amylose chain, and the high adsorptive capacity of this complex appears to be due to hydrophobic Interactions (1 6). 

Off-line iodine complexing is a frequently used method to characterize the SEC fractions. Amylose-iodine and iodine-amylopectin complex have a maximum absorbance at about 658 and 546 nm, respectively. Recently, Suortti and Pessa (63) demonstrated that is is possible to do iodine complexing detection on-line, such as that shown in Figure 4. Photodiode array (PDA) ultraviolet (UV) detectors are readily available now. PDA can take the UV spectrum of the eluant on the fly. The information is stored in the computer. After the run, a contour plot or three-dimensional plot can be shown on the screen or printed out. Iodine complexing with PDA detection can be a very useful technique for characterizing starch samples. 

Amylose is usually quantified by the iodine colorimetric assay in which iodine binds with amylose to produce a blue-colored complex. The starch is gelatinized with NaOH, neutralized, and reacted with iodine. The amount of amylose is related to absorbance at 620 nm. Amylopectin is usually determined by difference. (100-% amylose)... 

Molecular Interactions. Various polysaccharides readily associate with other substances, including bile acids and cholesterol, proteins, small organic molecules, inorganic salts, and ions. Anionic polysaccharides form salts and chelate complexes with cations some neutral polysaccharides form complexes with inorganic salts and some interactions are stmcture specific. Starch amylose and the linear branches of amylopectin form inclusion complexes with several classes of polar molecules, including fatty acids, glycerides, alcohols, esters, ketones, and iodine/iodide. The absorbed molecule occupies the cavity of the amylose helix, which has the capacity to expand somewhat to accommodate larger molecules. The starch—Hpid complex is important in food systems. Whether similar inclusion complexes can form with any of the dietary fiber components is not known. 

Iodide and iodate ions react under the influence of protons to yield iodine molecules which react with amylose to yield a blue clathrate complex ... 

Polycrystalline and well-oriented specimens of pure amylose have been trapped both in the A- and B-forms of starch, and their diffraction patterns84-85 are suitable for detailed structure analysis. Further, amylose can be regenerated in the presence of solvents or complexed with such molecules as alcohols, fatty acids, and iodine the molecular structures and crystalline arrangements in these materials are classified under V-amylose. When amylose complexes with alkali or such salts as KBr, the resulting structures86 are surprisingly far from those of V-amyloses. 

The yield is higher in basic solution in the presence of an oxidizing agent. Iodine forms a blue complex with P-amylose in starch. A hnear array of I5 species consisting of I2 -1 - I2 units bound to the amylose hehx causes blue color formation. 

Amylose [9005-82-7] (CgHjoOsln (for use in iodine complex formation). Amylopectin was removed from impure amylose by dispersing in aqueous 15% pyridine at 80-90 (concn 0.6-0.7%) and leaving the soln stand at 44-45" for 7 days. The ppte was re-dispersed and recrystd during 5 days. After a further dispersion in 15% pyridine, it was cooled to 45°, allowed to stand at this temperature for 12hours, then cooled to 25° and left for a further lOhours. The combined ppte was dispersed in warm water, ppted with EtOH, washed with absolute EtOH, and vacuum dried [Foster and Paschall JACS 75 1181 7955]. 

I hen iodine is mixed with starch, I the amylose stTands coil around the iodine molecules, forming a starch-iodine complex that has a characteristic dark blue color. The more starch present in a solution, the deeper the blue. The formation of this color is used to identify the presence of starch. In this activity, you will use an iodine solution to test for the presence of amylose and the amylose-digesting action of your saliva. 

The amylose-iodine complex is shown here. Amylase, an enzyme in your saliva, broke down the amylose in the solution you spit into, meaning there is less starch present to react with the iodine and consequently a lighter blue solution. 

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