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The denitrification process is a complex process that can be understood in two ways:

Broad Meaning: Denitrification is any denitrification process that results in the formation of more difficult to reduce compounds (nitrite, ammonia) nitrogen-containing organic compounds.

Narrow meaning: A denitrification process whose end product is the formation of molecular nitrogen.

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The denitrification process occurs in two different directions. That is, direct denitrification and indirect denitrification.

1. Direct denitrification

Direct denitrification is caused by many different species of microorganisms. Among them are the following species: Chromobacterium denitrificans – This species does not produce spores, they are facultative anaerobes. They have the ability to reduce nitrate to free N.

Achromobacter stutzeri: Often forms long chains, has the ability to coagulate milk and is capable of fermenting sugars to form vapors, growing on peptone media, forming HS. When grown under anaerobic conditions, they reduce nitrate.

Pseudomonas fluorescens: A motile bacillus. They hardly form chains.

Bact. Pyocyaneum: They participate in the reduction of nitrate and nitrite, to the free nitrogen molecule, and form a blue pigment in the environment.

The mechanism of the process can occur in 3 different cases:

* Reduce nitric acid to nitrite acid. Many saprophytic bacteria and fungi can reduce nitric acid but only nitrite acid

HNO + 2H -> HNO+ HO

* Some bacteria can reduce nitrate to NH

HNO + 8H -> NH + 3HO

* Many other species of microorganisms can reduce HNO to free N. This process can go through a number of different intermediate stages. We can summarize as follows:

2HNO -> 2HNO -> 2HNO -> N

These denitrification processes are energetically significant. The bacteria involved in denitrification are facultative respirators. In aerated conditions they use CO as a H acceptor. In anaerobic conditions they use nitrate for this task.

For example, during their anaerobic respiration, combined with denitrification occurs as follows:

1) CHO + 6HO + 12 dehydrogenaza = 6CO  + 12 dehy-H

2) 4NO + 12 dehy-H = 12HO + 2N + 12 dehydrogenaza

The general summary is as follows:

CHO + 4-HNO = 6CO+ 6HO + 2N + 420 Cal


– The denitrification process causes a loss of nitrogen in the soil, thereby damaging agricultural production. In anaerobic cases and when we carry out composting, the denitrification process occurs very strongly, the pH suitable for this process is neutral or alkaline pH = 7 – 8,2.

– In the food industry, the process of denitrification to nitrite is used in food production such as sausages, sausages, hams. The reddish-pink color of these varieties is due to the compound of nitrite with the meat colorant mioglobin. To form that compound, nitrite or nitrate is added to minced meat or brine. If nitrate is used, it must first be reduced by microorganisms to nitrite. The nitrite then combines with mioglobin and with hemoglobin to form nitrosomyoglobin and nitrosohemoglobin which is bright red (mainly due to the (NO) effect). Through heat treatment these substances convert to nitrosochromogens with a pink color, so they are widely used in the meat processing industry. In addition, nitrite also preserves the sensory value of fish meat, such as the characteristic flavor of salted fish meat.

However, if used in excess, it will be harmful to the human body. Because then they will react with amines to form nitrosamines according to the following reaction:


Nitrosamine often causes shortened life, weight loss and in many cases can cause cancer. Therefore, it is necessary to pay attention to the following aspects:

– Under no circumstances should nitrites or nitrates be added to children’s food

– Must be familiar with the regulations on the dosage of nitrate and nitrite when using that are allowed.

– There must be a person in charge of mixing according to a certain ratio. Permissible dosages in some countries are as follows: In the Soviet Union 75ppm nitrite and 100ppm nitrate in meat products and in finished products should not exceed 1530ppm. In the US 3.5 oz (1oz = 28.35g) sodium nitrate or potassium nitrate per 100 lb (1lb = 45kg) of meat (if hard meat is used) and 2.75 oz for 100 lb if tender. If sodium nitrate and potassium nitrate are used, the dosage of 1 oz for 100 lb of hard meat is 0.25 oz for 100 lb of tender meat.

– Generally it should not be more than 0.30% nitrate i.e. 0.3 kg for 100 kg of meat and 0.020% of nitrite i.e. 0.020 kg for 100 kg of meat.

2. Indirect denitrification

It is also a process that loses nitrogen content in the soil because nitrogen compounds are converted to N. The final stage of this process is purely chemical reactions that occur between nitrogen acids and amino acid compounds. and amide


R-CO-NH + O = N-OH -> RCOOH + N + HO

In this case, microorganisms only have an indirect effect of forming a.nitrogen (mostly due to denitrification) amino acids and amides.

For agriculture, the indirect denitrification process does not have much meaning because in soil, most of the reactions are alkaline, but the reaction requires acids.

Source of material: “Microbiological Technology – Author: Nguyen Duc Luong”

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