---
title: Iodine reagent
description: "Iodine reagent is used to detect the presence of starch in a growth medium. When it is added to [starch agar plates](https://vumicro.com/docs/starch-agar/), the iodine reagent combines with starch in the medium to produce a blue-brown color. Bacteria producing [alpha-amylase](https://vumicro.com/docs/starch-hydrolysis-test/), an…"
url: "https://vumicro.com/docs/iodine-reagent/"
updated: "2022-06-17"
category: Reference Library / Reagents, Chemicals, Stains
---

# Iodine reagent

Iodine reagent is used to detect the presence of starch in a growth medium. When it is added to [starch agar plates](https://vumicro.com/docs/starch-agar/), the iodine reagent combines with starch in the medium to produce a blue-brown color.

Bacteria producing [alpha-amylase](https://vumicro.com/docs/starch-hydrolysis-test/), an enzyme destroying starch, exhibit clear halos under their growth indicating that the starch has been digested. When iodine reagent is added to an overnight culture of a microbe unable to break down starch, the medium is converted to a uniformly blue-brown color.

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