---
title: Starch agar
description: "## What is this medium used for?   Starch agar is a general-purpose, nutrient medium used for the cultivation of microbes. Inclusion of starch makes it a rich medium for those bacteria possessing the enzyme [alpha-amylase](https://vumicro.com/docs/starch-hydrolysis-test/), which breaks starch down to…"
url: "https://vumicro.com/es/docs/starch-agar/"
updated: "2022-06-17"
category: Reference Library / Media
---

# Starch agar

## What is this medium used for?  

Starch agar is a general-purpose, nutrient medium used for the cultivation of microbes. Inclusion of starch makes it a rich medium for those bacteria possessing the enzyme [alpha-amylase](https://vumicro.com/docs/starch-hydrolysis-test/), which breaks starch down to its component glucose molecules. This medium, therefore, is useful for the detection of alpha-amylase.

## How is the presence of alpha-amylase determined?  

Starch combines with [iodine](https://vumicro.com/docs/iodine-reagent/) to form a blue-brown color. If the microbe produces alpha-amylase, the medium in the vicinity of the growth remains amber, indicating that starch near the growth was digested by the alpha-amylase produced by the microbes.

## What is the content of this medium?  

Starch agar consists of heat-stable digestive products of proteins (called peptones), as would be found in nutrient agar. These provide amino acids, minerals, and other nutrients used by a wide variety of bacteria for growth. In addition, the medium contains soluble starch.

## How is the starch hydrolysis performed?  

For information on how to determine if a microbe produces the enzyme alpha-amylase, refer to the [starch hydrolysis test](https://vumicro.com/docs/starch-hydrolysis-test/).

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