The Specific Iodine-Reaction of Sweet-Potato Starch cased by Some Microbes

Part 5. Difference of an Enzyme which causes the Reversion of Starch-Iodine Color Reaction from Isoamylase

Abstract

By comparing the action of α-amylase from Aspergillus candidus var. amylolyticus on soluble glutinous-rice starch or glycogen with that of. yeast of isoamylase on the same substrates, it was confirmed that these enzymes were different from each other.
When the former enzyme is added to the sol. of soluble glutinous-rice starch, very little amount of amyolse which is contained in the substrate is brought to helical structure around the amylose precipitants, especially the free fatty acid molecules, and the micells of the helical chains are formed. These micells are resistant against the enzyme action and remain intact in the solution during the digestion process. But the main part of the substrate consists of soluble amylopectin, which does not form micells, is digested rapidly to dextrins. Therefore, the original deep red color of starch-iodine complex turns to reddish brown and then brown, gradually, and at the same time, the amount of reducing sugars increases. Then, the remaining micells of the helical amylose chaines become the main substrate for starch-iodine complex, and the solution shows pure light blue coloration by addition of iodine 'solution. Glycogen, which contains no amylose fraction at all, does not show blue coloration by addition of iodine during the digestion by this enzyme.
On the other hand, since isoamylase mainly breaks down the α-1, 6-glucosidic linkages of amylopectin or glycogen, this enzyme catalyzes the production of amylose-like polysaccharides in the yield of 10 per cent or more from soluble glutinous-rice starch which contains only trace of amylose and it makes the glycogen-iodine coloration to change from brown to reddish violet.