Botany · Ch 8 — Biomolecules
Test for Starch
Test for Starch
The presence of starch is tested for by adding a solution of iodine dissolved in potassium iodide (an iodine-potassium iodide solution) to the sample. Iodine molecules fit precisely into the coiled helical structure of the starch molecule (specifically the amylose helix), forming a starch-tri-iodide complex that produces a distinctive blue-black colour. This colour change is highly specific to the helical arrangement of starch and does not occur with most other carbohydrates, which is why it remains the standard simple test for starch in both food samples (e.g., testi …
What this figure shows. Three panels showing the iodine starch test: (a) the test performed on a cut potato surface, (b) the test at varied starch concentrations, (c) a close-up schematic of iodine (tri-iodide ion) molecules fitting inside a coiled glucose (starch) chain, produc …