Coloration with iodine

Cultures of B. subtilis were introduced into the stems of young potato plants by Suit and Hibbert104 in an attempt to bring about replacement of starch by another polysaccharide. Sections of some of the resulting potatoes gave little or no color with iodine, and were provisionally designated starchless potatoes. However, based on analogy with recent developments in starch chemistry, it seems probable that the starchless potato was free from amylose, and contained only amylopectin. 

The amylase of Aspergillus oryzae causes a very rapid decrease in the viscosity of its substrates and a very rapid disappearance from its reaction mixtures of products which give color with iodine. When examined under favorable conditions71 at 40° with Lintner s soluble potato starch, the achroic point was reached with highly purified maltase-free amylase when approximately 12% of the glucose linkages of the substrate had been ruptured. 

Time (minutes) Color with iodine Theoretical maltose from reducing valuea Glucose linkages hydro- lyzed Fermentable sugar Dextrins ... 

Each of these amylases causes a rapid decrease in the viscosity of starch pastes and the rapid disappearance from its reaction mixtures of products that give color with iodine. During the early stages of the hydrolysis of starch, the relative decrease in the viscosity of the substrates for hydrolysates of equivalent reducing value is most marked... 

Nitrostarch gives no color with iodine. It is insoluble in water and does not gelatinize to form a paste as starch does when it is boiled with water. It is not notably hygroscopic, but may take Up 1 or 2% of moisture from a damp atmosphere. It is soluble in acetone. The varieties of nitrostarch which are soluble in ether-alcohol contain about the same amounts of nitrogen as the varieties of nitrocellulose which dissolve in that mixed solvent. Nitrostarch does not form a good film or tough colloid as nitrocellulose does. 

The glycogen obtained should be a white, amorphous powder and its aqueous solution should have a marked white opalescence, should not reduce Fehling s solution and should give an intense burgundy-red coloration with iodine. 

Solution of starch Reducibility PH Electrical conductivity (10-5 dm-3) Color with iodine... 

Color with iodine Dark blue Purple... 

Chain Length Color with Iodine Absorption Peak, Ana., nm... 

The analyses of heartwood and sapwood hemicellulose-A (Table VIII) were similar, and for both there was found a ratio of 11 anhydro-D-xylose units to 1 0-methylhexuronic acid unit. However, sapwood hemicellulose-A gave a blue color with iodine, but heartwood hemicellulose-A did not. Furthermore, hemicellulose-A from sapwood was less stable toward acid hydrolysis than was that from heartwood. ... 

Treatment of hemicellulose-A from sapwood with Takadiastase, for 44 hours, caused the blue color (with iodine) to disappear, and yielded D-glu-... 

Hemicellulose-B(Table V) from sapwood gave a blue color with iodine, which disappeared after treatment with Takadiastase under carefully controlled conditions. The solution was found to contain n-glucose, and its reducing value was equivalent to 24.6% of hexosan. On the basis of analytical data, heartwood hemicellulose-B appeared to be similar in constitution to the polysaccharide (6 anhydro-n-xylose units and 1 0-methyl-hexuronic acid per structural unit) isolated- after prolonged enzymic hydrolysis of heartwood hemicellulose-A. 

Fraction Yield in per cent Color with iodine [ Id Mol. wt. P, % Maltose, % ... 

TimCj min. Color with iodine Hydrolysis, % D-Glucose, % Maltose -h malto-Iriose, % a-Dextrins ... 

Time, hr. Relative viscosity Hydrolysis, % Color with iodine Crystals with iodine Ferment- able sugar, % MaUoae by amylase, % Linkages ruptured in dextri-mization, %... 

---