Prof. Dr. Sevgi ERTUĞRUL KARATAY

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Prof. Dr. Sevgi ERTUĞRUL KARATAY

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Biochemical Tests Fermentation Tests

Fermentation is a biochemical reaction where

phosphorylation occurs at the level of the substrate, which does not require oxygen molecules for energy

production.

Anaerobic, facultative anaerobic and microaerophilic microorganisms.

At the end of fermentation, products such as ethanol,

lactic acid, butanol, acetone are formed.

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Fermentation Tests

Clostridium species: Butanol, ethanol, acetone

Yeasts such as Saccharomyces cerevisiae or bacteria such as Zymomonas mobilis ethanol

Bacteria such as Lactobacillus pentosus can produce

lactic acid.

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Fermentation Tests

When these tests are done qualitatively, sugars and indicator substances that microorganisms can ferment

are usually used.

These fermentable sugars can be glucose, lactose,

inulin etc.

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Fermentation Tests

Indicator Acidic environment Basic Environment

Bromtimol blue Yellow Blue

Bromcresol purple Yellow Purple

Phenol red Yellow Red-Pink

When the pH of the medium decreases during fermentation, the color of the indicator

dyes changes. Thus, the presence of fermentation can be understood.

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Fermentation Tests

During fermentation tests, gas may also form (such as CO

2

). The presence of these gases can be determined

by durham tube.

When the Durham tube is placed in the liquid medium in an inverse direction, if gas is produced during

fermentation, gas is formed in the upper part of the

tube which is visibly visible.

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Fermentasyon Testleri

1) For fermentation test, phenol red is placed on four nutrient broth media containing glucose, sucrose,

lactose and xylose.

2) Durham tubes are placed on the media.

3) Each of the bacteria Escherichia coli , Staphylococcus aureus , Pseudomonas aeruginosa , Bacillus subti lis are

planted on these media with aseptically.

4) Microorganisms are allowed to incubate at 37 ºC for

24 hours.

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Fermentation Tests

Glucose Lactose Sucrose Xylose Gas

production

E. coli

S. Aureus

P. aeruginosa

B. subtilis

Please fill the table below according to results.

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Fermentation Tests

Important note:

In fermentation tests, the experiment should be followed periodically and the experiment should be

terminated when color change is observed.

If the experiment is continued, the peptons in the medium are used by the microorganisms and the pH

increases again. As a result of the pH increasing, the colors of the indicator substances return to their original state. In this case a false negative

result is obtained.