Carbohydrate Fermentation Test Introduction

Many of the biochemical test is used to detect the nature of the bacteria to detect their ability of utilizing the enzymes in their medium.

Carbohydrate fermentation test is one of the biochemical tests, which is used to detect the ability of a bacterium to use carbohydrate.

Carbohydrate Fermentation Test helps in testing the presence of an acid or a gas produced during the fermentation of a carbohydrate.

What is Carbohydrate Fermentation Test?

Carbohydrates are one of the organic molecules that comprises of carbon, Hydrogen and Oxygen in the respected ratio of CH2O.

Carbohydrates are classified into three types based on their structure and the number of carbon atoms it is present.

The types include monosaccharides and polysaccharides. The energy is released from the carbohydrates during the process of the catabolism, which results in the breakdown of these complex organic molecules.

Whereas this power for breaking carbohydrate comes from the micro-organisms like bacteria, yeast and fungi. However, these utilizations of the carbohydrate and its process of breakdown is different depending upon the enzyme system of the respective organism.

The pattern of fermentation is the characteristic species of certain organisms.

Due to these reasons, the property of the fermentative reaction is used extensively for differentiating the micro-organisms.

Carbohydrate Fermentation Test Objective

The main aim of the test is to detect the ability of the micro-organisms to ferment the carbohydrate and to produce the products of organic acids.

To determine the capability of the micro-organisms to synthesis gaseous and the fermentative products.

Carbohydrate Fermentation Test Principle

Carbohydrate fermentation is one the process in where the micro-organism produces energy in the form of Adenosine Triphosphate, ATP. Which is one the vital source of energy.

When glucose enters a cell, it catabolizes aerobically, where the oxygen molecule serves as a final electron acceptor.

In case of anaerobic respiration, the inorganic irons serve as the electron acceptors.

The metabolic end product formed after fermenting the carbohydrate results in organic acid and gaseous products.

Fermentative dehydration of the carbohydrates by the micro-organisms in the presence of oxygen is carried out in the fermentation tubes, which is known as Durham tube, which helps in detecting the production of gas.

Generally, a fermentation process is composed of basal medium which contains specific carbohydrates along with the pH indicator.

During fermentation of a carbohydrates, organic products are obtained. During these processes of metabolism there will a change in color of the medium.

This color change occurs only when a sufficient amount of acid is produced, as the organism utilize the peptones produced by the alkaline by products.

Thus, the degradation of the peptones in the culture results in production of the alkaline end products, which results in change in color of the culture from yellow to pink.

Carbohydrate Fermentation Test Procedure

I. Preparation of carbohydrate fermentation broth:

Initially, trypticase is weighed and dissolved along with the Sodium chloride and phenol red in about of 100 ml of distilled water and it is transferred into a conical flask.

About 1 % of the desired carbohydrate is then added into all the flasks.

Further Durham tubes is inserted into all the tubes in an inverted position.

Tubes should be filled fully.

Then it is sterilized in an autoclave at a temperature of about 115ºC for 15 minutes.

Here it should be noted that phenol red carbohydrate fermentation broth is should not be overheated, as it results in breaking the molecules and it forms compounds with a characteristic flavor and color.

This process is usually known a caramelizing of the sugar.

Then the sugar is transferred into the screw capped tubes or in the fermentation tubes and it is labelled properly.

II. Inoculation of bacterial culture into the fermentation tubes:

About one drop of inoculation is collected from the 18 to 24-hour culture broth and it is inoculated into a tube in an aseptic condition.

Then the tubes are inoculated at a temperature of about 37ºC for about 18 to 24 hours and they are examined for the production of acid and gas.

Carbohydrate Fermentation Test Result

Observation	Result	Interpretation
Change in color of the medium from pink to yellow color	It results in acid production	Organism ferments the given carbohydrate and it produces organic acids which reduces the pH of the medium and turns the medium into the acidic medium
The change in color of the medium to yellow color and there will be a production of gas in the Durham tube	It results in gas and acid production	Here, the organism ferments carbohydrates and the organic acids and it also releases gas and it is determined by air bubbles present in the medium in an inverted Durham tube.
There will be no change in color and the medium remains same	No fermentation takes place	Here the organism does not utilize the available carbohydrate and it grows by means of using the other sources present in the culture medium.