FERMENTATION

From Big Medical Encyclopedia

FERMENTATION — set of processes of enzymatic transformation of the carbohydrates which are carried out in anaerobic conditions. Is B. an internal oxidation-reduction process, with the help to-rogo many organisms receive chemical energy from glucose and other substances for lack of molecular oxygen. B. it is accepted to consider as the elementary form biol, the mechanism providing energy from nutrients.

A role of an end product at B. is played usually by some organic molecule which is formed during the process of B. (alcohol, milk to - that, oil to - that, etc.). The chemical nature of these products depends first of all on the species of microorganism which is carrying out anaerobic transformation of carbohydrates. Also conditions of course of B. depending on which the same microorganism carries out B. not only with various speed, but also with formation of various products are of great importance.

The products which are formed during B. are partially used by microorganisms in the course of their life activity (development, growth, accumulation of the general biomass). The chemical transformations of initial substrate happening during B. are followed by use a nek-swarm of a part of the chemical (free) energy which is contained in it for satisfaction of need of an organism for energy and its accumulation in the form of high-energy (vysokoergichesky) connections which major representative is adenosine triphosphoric acid (see). Thus, B. represents one of types of energy balance, feature to-rogo is a low use factor of the free energy which is contained in molecules of the organic matter which is exposed B. Low power performance is caused by the fact that in the course of B. free oxygen is not used.

The beginning of intensive studying of B. is connected with the description of yeast cells [Kanyar-Latur (V. S. Cagniard-Latour) in France and T. Shvann in Germany, 1836 — 1838]. Among the scientists studying it it is necessary to call L. Pasteur and 10. Libikh. Pasteur who called B. «life without oxygen» considered that it can be caused only by living yeast cells. Contrary to it Libikh considered fermentation of sugar as the composite chemical reaction which is not demanding participation of live organisms. The long dispute over this question having not only purely scientific, but also philosophical value, received the final decision as a result of works as M. M. Manasseina (1871) and in particular E. Bukhnera (1897), shown ability of acellular yeast juice to cause alcoholic fermentation. Thus, it was proved that B. is the enzymatic process proceeding and without participation of living cells.

The further research of the nature of B. showed that the whole fermental systems combined earlier under the general name «zymases» (take part in B.'s processes see. Enzymes ). In parallel there was a clarification of the chemical nature of the products which are formed at B.

The outstanding role in the solution of these complex challenges was played by researches of the Russian and Soviet scientists (A. N. Lebedev, L. A. Ivanov, V. I. Palladiya, S. P. Kostychev, Ya. O. Parnas, etc.), as well as foreign [A. Harden, K. Neyberg, O. Meyergof, G. Embden, etc.]. In particular, A. N. Lebedev offered new, easier way of receiving cell-free fermental preparations from yeast by an autolysis (self-digestion). Fundamental value for clarification of chemism of B. had opening of L. A. Ivanov who showed (1905) that at spirit B. not the free molecule of sugar, but connection of the last with phosphoric to - that is exposed to disintegration (a fosforilirovanny molecule of sugar). The subsequent researches not only confirmed L. A. Ivanov's conclusions, but also allowed to be convinced that reactions of phosphorylation at B. possess a key role (see. Glycolysis ).

Depending on the nature of the end product which is formed during process distinguish several types B.

Spirit fermentation

Spirit fermentation it is carried out by so-called drozhzhepodobny organisms (Monilia, Oidium, etc.), and also nek-ry of mold fungi (e.g., mukorovy).

Also cells of the higher plants are capable to produce alcohol if they are in the environment deprived of oxygen. In these conditions oxidizing exchange of plants is carried out till the ways close to spirit B. Nakonets, in some fabrics of the higher plants (e.g., cells of apical points, or so-called meristems) formation of alcohol is observed also in the conditions of full security with oxygen. Such processes are called aerobic fermentation, edges by the chemical nature also comes nearer to spirit B.

Spirit fermentation is expressed by the overall equation of reaction: With 6 H 12 O 6 = 2CO 2 + 2C 2 H 5 OH.

Follows from it that at full fermentation 1 asking hexoses are formed 2 asking carbon dioxide gas and 2 asking alcohol. The amount of the free energy realized during this process shall make theoretically 56 kcal on 1 mol of the fermented hexose that makes only an insignificant part of that energy output which takes place at normal aerobic respiration (see. Aerobes ). Thereof for obtaining the same amount of energy to anaerobic organisms (see. Anaerobe bacterias ) it is necessary to spend at least by 10 times bigger amount of sugars, than to aerobic organisms.

The overall equation of spirit B. does not consider that, in addition to alcohol and carbon dioxide gas, during B. also some other connections are formed in insignificant quantities. Treat them amyl alcohol (see), butyl alcohol (see) y some other, in total forming so-called. fusel oils (see). Among spirit B.'s products find also acetic aldehyde, amber to - that and some other the connections impacting specific aroma and relish to wine, beer and other alcoholic drinks.

At spirit B. molecules of sugars of various degree of complexity are used. The easiest yeast ferments glucose and fructose, it is much worse mannose and especially a galactose. Sucrose and a maltose are fermented only after preliminary hydrolysis. Only special types of yeast containing the enzyme hydrolyzing this disaccharide with formation of glucose and a galactose are capable to ferment lactose.

In the presence in the environment of oxygen power exchange of yeast is carried out on the way of the normal aerobic transformation allowing to spend sugar much more economically. The influence of oxygen preserving sugar was for the first time revealed L. Pasteur in this connection it began to be called as Pasteur's effect.

The first stages of transformations, the Crimea is exposed glucose at spirit B., consist in activation of a molecule of sugar. Activation is carried out gradually, through a number of the separate reactions which are consistently replacing each other. The first step of increase in reactivity of a molecule of glucose is formation of its phosphoric ether. A source phosphoric to - you become a molecule of adenosinetriphosphate (ATP), edge, giving this group, turns into adenosinediphosphate (ADF). Transfer of the rest of phosphate from ATP on glucose is carried out with the participation of enzyme hexokinase (see).

This stage is connected with energy consumption of one energy-rich bond of molecule ATP.

The following stage consists in an isomerization of a molecule a glyukozo-6-fos-veil and its transformation into fruktozo-6-phosphate. Process carries out enzyme of a glyukozofosfatizomeraz [KF 5. 3. 1. 9] which is found both in yeast, and in many other microorganisms and in fabrics of a large number of different types of plants and animals. Activation of fruktozo-6-phosphate is reached by accession to a molecule of one more rest phosphoric to - you and formations of fruktozo-1,6-diphosphate.

A source of phosphate and the energy necessary for this reaction, molecule ATP also serves. Reaction is catalyzed by enzyme fosfofruktokinazy [To F 2. 7. 1. 11]. The subsequent stage is education from a molecule of fruktozo-1,6-diphosphate of two phosphotrioses — a dioksiatsetonfosfat and a glitseraldegidfosfat (GAF). The enzyme catalyzing this reaction is called zymohexase (see).

Due to the features of the fermental systems participating in spirit B., from two called phosphotrioses only GAF participates in further transformations that would have to cause loss for B.'s process of a half of an initial molecule of glucose. However this loss is prevented thanks to presence at a cell of specific enzyme — fosfotriozoizomeraza, catalyzing a reversible test: dioksiatsetonfosfat <-> glitseraldegidfosfat. Thereby the possibility of use of a molecule of sugar completely is provided.

Oxidation of GAF is catalyzed by glitseraldegidfosfatdegidrogenazy (GAFD) and leads to formation of high-energy connection — 1,3 diphosphoglycerates (1,3 DFG). The general equation of reaction can be presented in the following form:

Reaction proceeds in several stages: one of SH group of GAFD participates in accession OVER + and formation of a complex — .

GAF joins this complex, its oxidation with formation of acylenzyme is carried out:

Then there is a transfer of hydrogen on OVER +  :

and transport of acyl for the rest of inorganic phosphate with education 1,3 diphosphoglycerates:

High-energy communication of the rest phosphoric to - you in a molecule 1,3 DFG provides a possibility of formation of ATP and 3-phosphoglyceric to - you:

Intramolecular movement of the rest of phosphate with the participation of phosphoglyceromutase leads to education 2-phosphoglyceric to - you, turning then in phosphoenolpyruvic to - that. At dephosphorylation phosphoenolpyruvic to - you and its turning into pyroracemic to - that (pyruvate) the chipping-off phosphate is transferred to ADF. Energy of two molecules ATP which are formed at this stage also represents that net gain in energy which the cell gets during all difficult chain of the processes described above. These processes have universal character and make a basis not only spirit, but also many other types of B., and first of all the gomofermentativny lactic B. called glycolysis (see). It is very important to note that the listed reactions lead to formation of the pyruvate used as substrate biol, oxidations (see. biological oxidation ) or breath.

In anaerobic conditions of transformation of pyruvate can go various ways. So, in case of spirit B. from pyruvate with the participation of enzyme of a decarboxylase CO2 is chipped off and acetaldehyde is formed:

CH 3 - CO-COOH → CO 2 + CH 3 CHO.

With the participation of specific enzyme (alcohol dehydrogenase) acetaldehyde is recovered with formation of an end product of spirit B. — alcohol. Hydrogen, necessary for this reaction, turns out from the recovered coenzyme — nicotinamide adenine dinucleotide, or NAD-N. If in any way to prevent recovery of acetaldehyde (e.g., having connected it with sodium bisulphite), then NAD-N hydrogen can react with the participation of enzyme of a glitserofosfatdegidrogenaza with phosphotrioses and lead to formation of glycerophosphate, and then and glycerin.

One of by-products of spirit B. is methyl-acetyl carbinol (acetylmethylcarbinol), CH 3 — CO — CHOH — CH 3 , formed at interaction of two molecules pyroracemic to - you or pyroracemic to - you with acetaldehyde:

CH 3 COCOOH + CH3COH → CH 3 COCHOH-CH 3 + CO 2 .

It is formed during so-called karboligazny reaction, edges is catalyzed by the enzymes emitted from yeast cells and from the higher plants. Methyl-acetyl carbinol is formed and at other types B. Atsetoin we will well dissolve in water, alcohol, ether. It is necessary to mention one of intermediate products of disintegration of carbohydrates at B. which also is derivative pyroracemic to - you. It is methyl glyoxal (CH 3 COCHO) which by the chemical nature represents aldehyde of pyruvate. During the heating with water or during the alkalifying of aqueous solutions methyl glyoxal turns in milk to - that. It can be formed also in the enzymatic way — at effect of specific enzyme of a metilglioksilaza. These connections are formed in very insignificant quantities.

Lactic fermentation

is Genetically connected with spirit B. the lactic fermentation having very much importance. In this case Pyroracemic to - that is not decarboxylized as at spirit B., and it is directly recovered with participation of a specific lactate dehydrogenase at the expense of NAD-N hydrogen.

Two groups of lactobacilli are known. Gomofermentativny bacteria which form only milk to - that enter the first of them. Lactobacilli of the second group (heteroenzymatic bacteria) form, except milk, also acetic to - that, and also alcohol (it is frequent in very significant amounts), carbon dioxide gas, ant to - that and some other products. The ratio between these products depends on many conditions (temperature, pH of the environment etc.). Often it is caused by joint activity of lactobacilli with yeast. Such joint «ferments» are often created artificially and widely used in bread baking — at preparation of rye bread, in production of grain kvass and a number of lactic products (cheese, kefir, curdled milk, koumiss and so forth). Big application is found by lactic B. in production milk to - you, for the food, textile and tanning industry used in a number of the industries.

Especially effectively lactic B. is carried out by thermophilic microbes like Thermobacterium cereale (earlier being called Lactobacillus delbrukii). It is formed milk to - that and as one of products of transformations of carbohydrates in muscular tissue of animals in the course of glycolysis.

Butyrate fermentation

Butyrate fermentation is carried out in most cases by strict anaerobes, i.e. the organisms capable to exist only in the oxygen-free environment.

During butyrate B. are formed not only oil to - that, but in certain cases and very significant amounts of alcohol, milk by N acetic acids, and also gaseous hydrogen and carbon dioxide gas. By means of butyrate B. decomposition of organic matters in the conditions of a shortcoming or total absence of oxygen (swamps, wetlands) is carried out. Great industrial value has the butyrate B. of pectic substances occurring at a lock of stalks of flax, hemp and receiving fibers. At the same time activity of the bacteria which are carrying out this type of B. needs to be prevented at different preparation of foodstuff in order to avoid deterioration in taste and damage of the last (e.g., rancidification of butter, a silo, etc.).

Spirit, milk and butyrate B. — the main types B.; other numerous types of B. represent or their various combinations, or are carried out on the basis of these or those products arising during a main type B. Tak, as a result acetic fermentation there is an oxidation of alcohol with the participation of oxygen of air. This type of B. is carried out by specific acetic-acid bacteriums. Overall equation of acetic B.:

CH 3 CH 2 OH + O 2 = CH 3 COOH + H 2 O.

After exhaustion of reserves of alcohol of a bacterium oxidize formed by it acetic to - that to carbon dioxide gas and water.

To B. which is carried out with participation About 2 , belongs gluconew acid fermentation — education gluconic to - you from glucose:

With 6 H 12 O 6 + H 2 O + O 2 → CH 2 OH(CHOH) 4 COOH + H 2 O 2 .

It we are called by nek-ry bacteria and mold mushrooms. Gluconic to - that is the valuable connection which is widely applied in medicine and pharm, the industries (see. Gluconic acid ).

Citrate fermentation it is carried out by nek-ry representatives of mold fungi; separate strains of Aspergillus niger are especially effective. Serves as an initial product Pyroracemic to - that, transformation a cut goes at the same time in two directions. A part it is oxidized in acetic whereas another, attaching carbonic acid, forms oxalacetic to - that. At condensation of acetic and oxalacetic acids it is formed lemon to - that. In addition to lemon to - you, at citrate B. butyl alcohol, acetone, and also alcohol, carbon dioxide gas and hydrogen are formed.

Butanolovo-atsetonovoye fermentation carry out anaerobic bacteria of Clostridium acetobutylicum. The staples which are formed during this type of B. — N - butyl alcohol, acetone, alcohol, carbonic acid, hydrogen. Acetoacetic to - that (CH 3 COCH 2 COOH) and the acetone which is formed at its decarboxylation (CH 3 COCH 3 ), and also β-hydroxy-butyric to - that to - that to - that make group of so-called acetone bodies (see. Ketone bodies ), which collect in blood and urine of animals at various morbid conditions and diseases (diabetes, starvation). In normal conditions these connections are oxidized with education harmless to an organism of carbonic acid and water.

High economic efficiency, purity of the valuable products received at B. are the cornerstone of more and more wide use of B. in the most various industries of the national economy.


Bibliography: Kretovich V. L. Fundamentals of phytochemistry, M., 1971; Mahler G. ikordes Yu. Fundamentals of biological chemistry, the lane with English, M., 1970; Rubin B. A. Course of phytophysiology, M., 1971; Reker E. Biopower mechanisms, the lane with English, M., 1967. bibliogr.; Shaposhnikov V. N. Industrial microbiology, M., 1948; H a s s i d W. Z. Transformation of sugars in plants, Ann. Rev. plant Physiol., v. 18, p. 253, 1967, bibliogr.

B. A. Rubin.

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