Starch-Water Complexes

APHA Method 4500-CL02-B, iodometric titration analysis, measures the concentration of chlorine dioxide in water by titration with iodide, which is reduced to form iodine. Iodine is then measured colorimetrically when a blue color forms from the production of a starch-iodine complex. The detection limit for this method is 20 pg/L (APHA 1998). 

Starch-iodine complexation is temperature dependent. At 50°C, the color is only one-tenth as intense as at 25°C. If maximum sensitivity is required, cooling in ice water is recommended.20 Organic solvents decrease the affinity of iodine for starch and markedly reduce the utility of the indicator. 

An accurately weighted amount of primary standard is dissolved in water containing an excess of potassium iodide. Upon acidification, stoichiometric amounts of iodine are liberated instantly, which are titrated with thiosulfate titrant of unknown strength, decolorizing the blue starch-iodine complex at the end point. With potassium iodate, the ionic reaction is as follows ... 

In the presence of excess water, the transition enthalpy (AHCX) of the rye starch-lipid complex was determined to be 0.84 J/g.25 For the nine different rye starches described above, the AHCX range was 0.3-0.6 J/g.8 These values are lower than those for wheat starch, thus supporting the lower lipid content of rye starch compared to wheat starch.24 Also, there were small differences in transition temperature at a water content of 60%, the range was 100.0-106.6°C. 

Lime gives a vdute turbidity on addition of saturated ammonium oxalate solution, and sulphates with barium chloride acidified with hydrochloric acid. A useful reagent for nitrites is metaphenylene diamine, 5 grams of which are dissolved in water, acidified with dilute sulphuric acid, and made up to one litre. It may be necessary to previously decolorise the solution with charcoal. If nitrites are present in the water to be tested, on addition of the diamine, a yellow colour is produced, either immediately or upon standing. Starch-iodide solution acidified with dilute sulphuric acid may also be used, the characteristic blue colour of the starch-iodine complex indicating nitrites, but this test is not altogether satisfactory. 

The blue starch iodine complex has been used from time immemorial as an indicator in aqueous iodometric titrations water is required for development of the blue color. The color sensitivity is decreased with increasing temperature and also with increasing concentration of ethanol [134]. Although one might imagine this to be evidence for a charge-transfer complex,... 

A method of determining airborne iodine has also been reported.241 Here, iodine is absorbed into 5% aqueous KI and spectrophotometrically determined at 590 nm in the form of its complex with starch. This method is selective with respect to bromine and chlorine, and the sensitivity of this method is 0.25 mg of I2 per m3 of air. The concentration of the, 31I isotope in water can be determined by a method involving isotope exchange in the starch-iodine complex.242 Flow-injection determination of ascorbic acid (0.1-40 mg/mL) has been proposed.243 Iodine is generated in the flow system as I3- ions, which are in turn exposed to starch to produce a steady signal at 350 and 580 nm. Ascorbic acid provides inversed maxima which are measured. This method is recommended for analysis of ascorbic acid in fruit juice, jam, and vitamin-C preparations. Use of the blue complex has also been reported for determination of sodium dichloro-isocyanurate in air.244 Obviously the blue reaction is applicable in the determination of amylose, amylopectin, and starch,245-252 as well as modified starches.245,253-255... 

The second point concerns water that is usually held by natural starch, that is, a state that can be considered as the natural starch-water inclusion complex. In this case also, the concentration of such water depends on the same factors as those just mentioned. Corresponding data are given in Table XIV. 

Studies by Rundle et al., which were reviewed by Szejtli and Augustat,382 point to the helical structure of amylose in aqueous solutions. The dimensions of the amylose helix are well recognized, and therefore the structural similarity of the turns of the helix to cyclomaltohexaose (a-cyclodextrin) is sound. The a-cyclodextrin-water complex contains two guest molecules of water inside the cavity.383 Therefore, it may be accepted that part of the constitutional water of starch is included inside the amylose helix. Indeed,... 

Starch-iron complexes are reported as biologically active sources of iron.627 628 In one report, it is warned that such complexes may produce sarcomas as a result of long-term exposure.629 Investigations630 have shown that, independently of the ferric salt used, the maximum capacity of the salt in starch is 2-7 mg%. Because pH 5.8 is more conducive to stability than low pH values (3 or lower), higher concentrations of ferric salt are not advisable. Shi Decheng631 recommended blending starch (100 g) with trisodium citrate (25g) and 2 M FeCl3 (500 mL) in water (2500 mL) at... 

Several observations indicate the formation of starch-protein complexes. For instance, starch precipitates serum proteins of rabbit, horse, sheep, and chicken.962 This observation seemingly indicates that the complexation has a rather universal character. On the other hand, the type of bonding of proteins from Triticum durum and Triticum sativum is specific for each of these varieties.963 The observed effects may not be associated with complex formation, but they can instead be attributed to the destruction of micelles by dehydration, followed by agglomeration.964 As in the case of starch complexes with sugars, the effect of proteins and cellulose derivatives on starch gelation can be assumed to be the result of the competition for water in solution. As a consequence, swelling is perturbed.965-968... 

A composition of starch, protein, and water constitutes a patented floccu-lant.1031 Coated paper, suitable for printing, may be prepared by coating it with a starch-soybean protein complex generated in situ on the paper surface.1032 Starch-protein complexes are also patented as additives that increase baking capacity.1033 1037... 

Solid-state cellulose can also be noncrystalline, sometimes called amorphous. Intermediate situations are also likely to be important but not well characterized. One example, nematic ordered cellulose has been described [230]. In most treatments that produce amorphous cellulose, the whole fiber is severely degraded. For example, decrystallization can be effected by ball milling, which leaves the cellulose as a fine dust. In this case, some crystalline structure can be recreated by placing the sample in a humid environment. Another approach uses phosphoric acid, which can dissolve the cellulose. Precipitation by dilution with water results in a material with very little crystallinity. There is some chance that the chain may adopt a different shape (a collapsed, sixfold helix) after phosphoric acid treatment. This was concluded because the cellulose stains blue with iodine (see Figure 5.12), similar to the sixfold amylose helix in the starch-iodine complex. 

A solution of sodium thiosulfate was standardized by dissolving 0.1210 g KIO3 (214.00 g/mol) in water, adding a large excess of KI, and acidifying with HCl. The liberated iodine required 41.64 mL of the thiosulfate solution to decolorize the blue starch/iodine complex. Calculate the molarity of the Na2S203. 

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 study of the Influence of solvents on the formation of the starch-lodlne-complex has revealed that the water requirement is not related to either the dipole moment or the dielectric constant of the solvent ( ). Moullk and Gupta have shown that surfactants and cosolvents, mainly destabilize the amylose-lodine-complex, and the overall polarity of the mixed medium is insufficient to systematize the solvent effect ( ). One et al have reported that the blue colour of the amylose-iodlne-complex is not formed in dimethyl sulphoxide-water mixtures containing less than 28 moles of water per litre (25). 

This complex behavior of the starch/water/modified silica system is also confirmed by calculations of the distribution function of the activation energy of relaxations (Figure 5.10b) showing that the... 

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