Interference of Ascorbic Acid with the Starch-lodine Reaction

Starch estimation in various plant tissues is accomplished usinga reaction between starch and iodine. We report that the starch-iodinereaction is strongly inhibited by ascorbic acid, a normal cellularconstituent of higher plants. The presence of 10^–4 M ascorbicacid in the reaction mixture caused an almost complete inhibitionof the starch-iodine reaction. This inhibition may be alleviatedby increasing the amounts of iodine-potassium iodide (IKI) inthe reaction mixture, suggesting the possibility that a complexis formed between ascorbic acid and iodine. Evidence for thiscomes from a shift in absorption maxima of ascorbic acid dueto addition of IKI. Starch-iodine reaction, ascorbic acid, interference