Purple starch

Starches can be separated into two major components, amylose and amylopectin, which exist in different proportions in various plants. Amylose, which is a straight-chain compound and is abundant in potato starch, gives a blue colour with iodine and the chain assumes a spiral form. Amylopectin, which has a branched-chain structure, forms a red-purple product, probably by adsorption. 

Potassium permanganate and iodine, which are important redox reagents, are both self-indicating, i.e. the colour of the reagent in each case is intense and will impart a perceptible colour to a solution when present in very small excess. One drop of a solution of potassium permanganate (0.02 mol dm 3) can be detected in a titrand solution of 100 cm3, and a similar amount of iodine by shaking the titrand with 5 cm3 of chloroform or carbon tetrachloride to produce an intense purple colour. Specific indicators react in a specific manner with one participant in the reaction. The best examples are starch, which produces an intense blue colour with iodine and potassium thiocyanate, which forms an intense red compound with iron(III). 

Suzuki, A., Shibanuma, K., Takeda, Y, Abe, J. and Hizukuri, S. (1994). Structures and pasting properties of potato starches from Jaga Kids Purple 90 and Red 90. Oyo Toshitsu Kagaku, 41,425-432. 

Following this discovery, several other bacteria were found to elaborate a-amylases that could digest potato starch granules an anaerobic Clostridium butyricum 206 a non-sulfur purple photosynthetic bacterium, Rhodopseudomonas gelatinosa 205 and two other Bacillus species.206,207... 

Starch can form an intense, brilliant, dark blue-, or violet-colored complex with iodine. The straight chain component of starch, the amylose, gives a blue color while the branched component, the amylopectin, yields a purple color. In the presence of iodine, the amylose forms helixes inside of which the iodine molecules assemble as long polyiodide chains. The helix-forming branches of amylopectin are much shorter than those of amylose. Therefore, the polyiodide chains are also much shorter in the amylopectin-iodine complex than in the amylose-iodine complex. The result is a different color (purple). When starch is hydrolyzed and broken down to small carbohydrate units, the iodine will not give a dark blue (or purple) color. The iodine test is used in this experiment to indicate the completion of the hydrolysis. 

Mercury nitride forms a chocolate colored powder, which is slowly decomposed by water. The dry nitride tarnishes in air, and is slowly decomposed in acidic media. The nitride is very explosive, and must be handled with extreme care. It detonates violently yielding a white flame with a bluish purple border, and also when heated. The salt can be detonated by rubbing it with a rounded glass stir rod—very friction sensitive. Mercury nitride also easily detonates by shock, or percussion. Handle with care never store dry keep submerged in a water free solvent such as kerosene in amber glass bottles in a cool place. It is advisable to desensitize mercury nitride with gum Arabic, paraffin wax, or starch immediately after preparation, and these mixtures should be carefully blended using a wood spoon or plastic spatula—metal and glass should be avoided. ... 

Cleaning Up Place dichloromethane solutions in the halogenated organic solvents container and organic solvents in the organic solvents container. The alumina should be placed in the alumina hazardous waste container. If it should be necessary to destroy 3-chloroperoxybenzoic acid, add it to an excess of an ice-cold solution of saturated sodium bisulfite in the hood. A peracid will give a positive starch/iodide test (blue-purple color). 

F, Cl, Br, J TLC silica gel + starch binder fluorescent reagent Visual + bromcresol-purple 1-2 Mg 310)... 

It is the amylose component of starch that gives the blue color when KI/I2 solution is added. To study the iodine-iodide color of amyloses of different d.p. values, maltodextrin-amylose molecules, with various avg. d.p. values from 6 to 568 were prepared by Bailey and Whelan [62], using phosphorylase, a-D-glucopyranosyl-1-phosphate, and maltohexaose. The colors of the various sized maltodextrins (1 mg) were observed when 10 1 (w/w) KI/I2 solution was added. The first color to be observed was faint red for avg. d.p. 12 a red-purple color was observed for avg. d.p. 31 a purple color was observed for avg. d.p. 40 and a blue color was observed for avg. d.p. 45. The increase in the blue value was linear as a function of avg. d.p. up to avg. d.p. 60 the absorbance at 645 nm then slowly increased and reached a maximum at avg. d.p. of 400. The intensity of the iodine/iodide color in the low molecular weight range was dependent on the concentration of the iodine. When the concentration of the iodine was increased 10-fold, the intensity was increased 50% [62]. 

The increased affinity of amylopectins for iodine is partly accounted for by the increase in exterior and interior chain-lengths. Other factors are probably involved as sweet corn polysaccharides (C. L. 12-13) bind more iodine than does glycogen, and glutinous rice-starch (C. L. 18 jS-amylo-lysis limit, 47 %) is stained red rather than purple with iodine. ... 

A) Molisch Test for Carbohydrates. Apply the test to small amounts of the following sucrose, starch, and paper fibers. Place in a test tube 2 ml of one per cent carbohydrate solution or dispersion. Add 2 drops of a 10 per cent solution of a-naphthol in alcohol, and mix. Add this carefully down the side of a tube containing 2 ml of concentrated sulfuric acid so that it will form a separate layer. Carbohydrates give a purple color at the junction of the two liquids. 

Test Paper from Hollyhock Flowers. Somo years ago Prof. Aiken, of tho University of Maryland, proposed paper stained with an infusion of the petals, os a substitute for litmus paper. His althrea paper is purplish-blue when dry acids impart a carmine hue, which is turned to bluish-green by alkalies, the neutral tint being purplish-blue it is superior in intensity of reaction to turmeric, and quite equal to litmus, and is not affected by light, as is tho case with tho latter. Tho alkaline reaction is produced in natural or atmospheric waters and tho presence of nitrites, which change tho red paper to purple, is indicated in greater dilution than with iodide starch. 

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