BUTYRIC FERMENTATION: PROCESS, ORGANISMS AND PRODUCTS - BIOLOGY - 2025

The butyric fermentation occurs when glucose from butyric acid is obtained as the major end product. It is carried out by certain bacteria under conditions of complete absence of oxygen and was discovered by Louis Pasteur, according to his note in a report in 1861 on experiments carried out in 1875.

Fermentation is a biological process by means of which a substance is transformed into a simpler one. It is a catabolic process, of degradation of nutrients to obtain an organic compound as a final product.

Louis Pasteur

This process does not require oxygen, it is anaerobic, and it is characteristic of some microorganisms such as bacteria and yeast. Fermentation also occurs in the cells of animals, especially when the cellular supply of oxygen is insufficient. It is an energetically low yielding process.

From the glucose molecule, using the Embden-Meyerhof-Parnas pathway (the most common glycolysis pathway), pyruvate is produced. Fermentations start from pyruvate, which is fermented into different products. Depending on the end products, there are different types of fermentation.

Butyric ferrmentation process

Butyric fermentation is defined as the degradation of glucose (C6H12O6) to produce butyric acid (C4H8O2) and gas, under anaerobic conditions and with low energy yield. It is characteristic for the production of unpleasant and putrid odors.

Butyric fermentation is carried out by Gram-positive spore-producing bacteria of the genus Clostridium, typically Clostridium butyricum, Clostridium tyrobutyricum, Clostridium thermobutyricum, in addition to Clostridium kluyveri and Clostridium pasteurianum.

However, other bacteria classified in the genera Butyrvibrio, Butyribacterium, Eubacterium, Fusobacterium, Megasphera and Sarcina have also been reported as butyrate producers.

In the fermentation process, glucose is catabolized to pyruvate, producing two moles of ATP and NADH. Pyruvate is subsequently fermented into various products, depending on the bacterial strain.

In the first instance, pyruvate becomes lactate and this becomes acetyl-CoA with the release of CO2. Subsequently, two acetyl-CoA molecules form acetoacetyl-CoA, which is then reduced to butyryl-CoA, through certain intermediate steps. Finally, Clostridium ferments the butyryl-CoA into butyric acid.

The enzymes phosphotransbutyrylase and butyrate kinase are the key enzymes for the production of butyrate. In the process of butyrate formation, 3 moles of ATP are formed.

Under exponential growth conditions, cells produce more acetate than butyrate, as one more mole of ATP is formed (4 in total).

At the end of exponential growth and entering the stationary phase, bacteria decrease acetate production and increase butyrate production, reducing the total concentration of hydrogen ions, balancing the acidic pH of the medium.

Organisms that carry out butyric fermentation

The most promising microorganism used for the bioproduction of butyric acid is C. tyrobutyricum. This species is capable of producing butyric acid with high selectivity and can tolerate high concentrations of this compound.

However, it can only ferment from very few carbohydrates, including glucose, xylose, fructose, and lactate.

C. butyricum can ferment many carbon sources, including hexoses, pentoses, glycerol, lignocellulose, molasses, potato starch, and cheese whey permeate.

However, the butyrate yields are much lower. In C. thermobutyricum, the range of fermentable carbohydrates is intermediate, but it does not metabolize sucrose or starch.

Biobutyrate-producing clostridia also produce several possible by-products, including acetate, H2, CO2, lactate, and other products, depending on the Clostridium species.

Fermentation of a glucose molecule by C. tyrobutyricum and C. butyricum can be expressed as follows:

Glucose → 0.85 Butyrate + 0.1 Acetate + 0.2 Lactate + 1.9 H2 + 1.8 CO2

Glucose → 0.8 Butyrate + 0.4 Acetate + 2.4 H2 + 2 CO2

The metabolic pathway of a microorganism during anaerobic fermentation is affected by several factors. In the case of bacteria of the genus Clostridium, producers of butyrate, the factors that mainly affect growth and fermentation performance are: glucose concentration in the medium, pH, partial pressure of hydrogen, acetate and butyrate.

These factors can influence the growth rate, the concentration of the final products and the distribution of the products.

products

The main product of butyric fermentation is a carboxylic acid, butyric acid, a short-chain four-carbon fatty acid (CH3CH2CH2COOH), also known as n-butanoic acid.

It has an unpleasant smell and a pungent taste, however it leaves a somewhat sweet taste in the mouth, similar to what happens with ether. Its presence is characteristic of rancid butter, being responsible for its unpleasant smell and taste, hence its name, which is derived from the Greek word for "butter."

However, certain butyric acid esters have a pleasant taste or odor, which is why they are used as additives in food, beverages, cosmetics, and the pharmaceutical industry.

Uses and applications of butyric acid

Biofuels

Butyric acid has many uses in different industries. There is currently great interest in using it as a precursor to biofuels.

Food and pharmaceutical industry

It also has important applications in the food and flavoring industries, due to its butter-like taste and texture.

In the pharmaceutical industry it is used as a component in various anticancer drugs and other therapeutic treatments, and butyrate esters are used in the production of perfumes, due to their fruity fragrance.

Cancer Research

Butyrate has been reported to have various effects on cell proliferation, apoptosis (programmed cell death), and differentiation.

However, different studies have given contrary results in terms of the effect of butyrate on colon cancer, giving rise to the so-called “butyrate paradox”.

Chemical synthesis

Microbial production of butyric acid is a preferable attractive alternative to chemical synthesis. The success of industrial implementation of bio-based chemicals is highly dependent on the cost of production / economic performance of the process.

Therefore, the industrial production of butyric acid by fermentation processes requires inexpensive raw material, high efficiency process performance, high product purity, and strong robustness of the producing strains.

References

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