Fermentation is difficult process breakdown of carbohydrates under the influence of enzymes secreted by various microorganisms, in most cases accompanied by the release of gaseous products (CO 2, H 2, etc.) and ultimately leading to the formation of substances such as ethanol, lactic acid, etc. Depending on the type of microorganisms and end products, several types of fermentation are distinguished:

Alcoholic fermentation: C 6 H 12 O 6 → 2CH 3 ─ CH 2 ─ OH + 2CO 2

Glucose Ethanol

Lactic acid fermentation: C 6 H 12 O 6 → 2CH 3 ─ CHOH ─ COOH

Glucose Lactic acid

Acetic acid fermentation: C 6 H 12 O 6 + 2O 2 → 2CH 3 ─ COOH + 2CO 2 + 2H 2 O

Glucose Acetic acid

Propionic acid fermentation: C 6 H 12 O 6 → 2CH 3 ─ CH 2 ─ COOH + O 2

Glucose Propionic Acid

Butyric fermentation: C 6 H 12 O 6 → CH 3 ─CH 2 ─CH 2 ─ COOH + 2CO 2 + 2H 2

Glucose Butyric acid

Citric acid fermentation: 2C 6 H 12 O 6 + 3O 2 → CH 2 ─ COOH

Glucose │

2HO ─ C ─ COOH + 4H 2 O

Lemon acid

Methane fermentation: C 6 H 12 O 6 → 3CH 4 + 3CO 2

Glucose Methane

Alcoholic fermentation is used in industry for the production of ethyl alcohol, lactic acid fermentation- v Food Industry for obtaining a variety of lactic acid products and in animal husbandry when ensiling feed. Acetic acid, propionic acid, butyric acid, lactic acid fermentation takes place in the ruminants. Methane fermentation causes tympania (bloating) in animals with a multichamber stomach. Alcoholic fermentation only hexoses are exposed, in contrast to other monosaccharides, such as pentoses. This is used to distinguish hexoses from pentoses. Maltose and sucrose are readily fermented by yeast, but lactose is not fermented by them. Yeast contains enzymes - maltase and sucrase, but no lactase enzyme. Lactose, under the influence of bacteria that break down it, can give alcoholic, lactic and butyric acid fermentation.

Assignment: Draw conclusions on the topic "Carbohydrates:

Session 5 - Protein structure

Purpose of the lesson: Examine the structure of proteins

Reagents: Protein solutions: egg and gelatin, 1% copper sulfate solution, 10% and 20% sodium hydroxide solutions, 0.2% ninhydrin solution, 0.5% lead acetate solution.

1. General qualitative reactions to proteins: biuret - to the peptide bond, ninhydrin - to the α-amino groups of amino acids

The principle of the method. Biuret reaction is a qualitative reaction to a peptide bond. The reaction is based on the formation of an intracomplex compound of copper ions with two peptide bonds acting as polydentate ligands. V alkaline environment the protein solution turns pink-violet when a dilute copper sulfate solution is added:

H 2 N-CH-CO-NH-CH-CO-NH-CH-CO-NH-CH-C = O + 2NaOH + Cu (OH) 2

R 1 R 2 R 3 R 4 OH

NH-CH-C = N-CH-C-N-CH-C -... 2-

R 4 O R 6 O 2Na +

NH-CH-C-N-CH-C = N-CH-C -...

The reaction is called biuret, since it is also characteristic of biuret, which consists of 2 urea molecules (NH 2 -CO-NH-CO-NH 2).

Progress. Biuret reaction. I ml of solutions of the studied proteins are poured into separate test tubes: egg white, gelatin, blood serum. Then add 1 ml 10 % solution NaOH and 2 drops of 5% solution CuS0 4. After stirring, in the presence of a peptide bond, a violet color appears in the test solutions.

Ninhydrin reaction... 10-12 drops of ninhydrin are added to 2 ml of the studied protein solutions, heated, a blue-violet color is observed - the product of the interaction of the amino group of amino acids with ninhydrin.

reduced ninhydrin

Condensation product colored blue-violet

FERMENTATION- a set of processes of enzymatic conversion of carbohydrates carried out under anaerobic conditions. B. is an internal redox process, with the help of which many organisms receive chem. energy from glucose and other substances in the absence of molecular oxygen. B. is considered to be the simplest form of biol, a mechanism that provides energy from nutrients.

The role of the final product in B. is usually played by some organic molecule formed in the course of the B. process itself (alcohol, milk to-that, oil to-that, etc.). Chem. the nature of these products depends primarily on the type of microorganism that carries out the anaerobic conversion of carbohydrates. Great importance B. also have conditions of flow, depending on which one and the same microorganism carries out B. not only at different rates, but also with the formation of different products.

The products formed in the course of biomass are partially used by the microorganisms themselves in the process of their vital activity (development, growth, accumulation of total biomass). Chem. transformations of the initial substrate, occurring in the course of B., are accompanied by the use of a certain part of the chemical contained in it. (free) energy to satisfy the body's need for energy and its accumulation in the form of energy-rich (high-energy) compounds, the most important representative of which is adenosine triphosphoric acid (see). Thus, B. is one of the types of energy metabolism, a feature of which is the low utilization rate of free energy contained in the molecules of organic matter exposed to B. Low energy efficiency is due to the fact that free oxygen is not used in the B. process. ...

The beginning of an intensive study of B. is associated with the description of yeast cells [Canyard-Latour (VS Cagniard-Latour) in France and T. Schwann in Germany, 1836-1838]. Among the scientists who studied it, one should name L. Pasteur and 10. Liebig. Pasteur, who called B. "life without oxygen," believed that it can only be caused by living yeast cells. In contrast, Liebig viewed sugar fermentation as a complex chemical. a reaction that does not require the participation of living organisms. The long dispute on this issue, which has not only purely scientific but also philosophical significance, was finally resolved as a result of the works of M.M.Manasseina (1871) and, in particular, E. Buchner (1897), who showed the ability of acellular yeast juice to induce alcoholic fermentation. Thus, it has been proven that fermentation is an enzymatic process that takes place without the participation of living cells.

Further study of the nature of B. showed that whole enzyme systems, previously united under the general name "zymases" (see Enzymes), take part in B.'s processes. In parallel, there was a clarification of chemical. the nature of the products formed during B.

An outstanding role in solving these complex problems was played by the research of Russian and Soviet scientists (A.N. Lebedev, L.A. Ivanov, V.I.Palladia, S.P. and foreign [A. Harden, K. Neuberg, O. Meyerhof, G. Embden, etc.]. In particular, A.N. Lebedev proposed a new, simpler method for obtaining acellular enzyme preparations from yeast by autolysis (self-digestion). The discovery of L.A. Ivanov, who showed (1905), that in alcoholic B., it is not the free sugar molecule that undergoes decomposition, but the combination of the latter with phosphoric acid (phosphorylated sugar molecule), is of fundamental importance for the elucidation of the chemistry of B. Subsequent studies not only confirmed the conclusions of L.A. Ivanov, but also made it possible to make sure that phosphorylation reactions in B. play a key role (see. Glycolysis).

Depending on the nature of the final product formed during the process, several types of B. are distinguished.

Alcoholic fermentation

Alcoholic fermentation is carried out so-called. yeast-like organisms (Monilia, Oidium, etc.), as well as some of the molds (for example, mucor).

The cells of higher plants can also produce alcohol if they are in an environment devoid of oxygen. Under these conditions, the oxidative metabolism of plants is carried out along a path close to alcoholic B. Finally, in some tissues of higher plants (for example, cells of growth points, or the so-called meristem), the formation of alcohol is also observed under conditions of complete oxygen supply. Such processes are called aerobic fermentation, edges in their chemical. nature also approaches alcoholic B.

Alcoholic fermentation is expressed by the general reaction equation: C 6 H 12 O 6 = 2CO 2 + 2C 2 H 5 OH.

It follows from this that with complete fermentation of 1 mole of hexose, 2 moles of carbon dioxide and 2 moles of ethyl alcohol are formed. The amount of free energy realized during this process should theoretically be 56 kcal per 1 mole of fermented hexose, which is only a small part of the energy output that occurs during normal aerobic respiration (see Aerobes). As a result, to obtain the same amount of energy, anaerobic organisms (see Anaerobes) need to spend at least 10 times more sugars than aerobic organisms.

The total equation of alcoholic fermentation does not take into account that, in addition to ethyl alcohol and carbon dioxide, certain other compounds are formed in the course of fermentation in small quantities. These include amyl alcohols (see), butyl alcohols (see) and some others, which together form the so-called. fusel oils (see). Acetaldehyde, amber to-that, and a number of other compounds that impart a specific aroma and taste to wine, beer, and other alcoholic beverages are also found among the products of alcoholic fermentation.

In alcoholic B., sugar molecules are used. varying degrees difficulties. Yeast ferments glucose and fructose most easily, mannose and especially galactose are much worse. Sucrose and maltose are fermented only after preliminary hydrolysis. Lactose can be fermented only by special types of yeast containing an enzyme that hydrolyzes this disaccharide to form glucose and galactose.

In the presence of oxygen in the environment, the energy exchange of yeast proceeds along the path of normal aerobic conversion, which makes it possible to spend sugar much more economically. The sugar-saving effect of oxygen was first discovered by L. Pasteur, in connection with which it became known as the Pasteur effect.

The first stages of transformations, a cut of glucose undergoes in alcoholic B., consist in the activation of a sugar molecule. Activation is carried out gradually, through a series of successively replacing individual reactions. The first step in increasing the reactivity of the glucose molecule is the formation of its phosphorus ester. The source of phosphoric to - you is the molecule of adenosine triphosphate (ATP), edges, giving this group, turns into adenosine diphosphate (ADP). The transfer of the remainder of phosphate from ATP to glucose is carried out with the participation of the enzyme hexokinase (see).

This stage is associated with the expenditure of energy of one high-energy bond of the ATP molecule.

The next step is to isomerize the glucose-6-phosphate molecule and convert it to fructose-6-phosphate. The process is carried out by the enzyme glucose phosphate isomerase [EC 5. 3. 1. 9], which is found both in yeast and in many other microorganisms and in the tissues of a large number different types plants and animals. Activation of fructose-6-phosphate is achieved by attaching another phosphoric acid residue to the molecule and the formation of fructose-1,6-diphosphate.

The source of phosphate and the energy required for this reaction is also the ATP molecule. The reaction is catalyzed by the enzyme phosphofructokinase [K F 2. 7. 1. 11]. The next stage is the formation of two phosphotriosis from the fructose-1,6-diphosphate molecule - dioxyacetone phosphate and glyceraldehyde phosphate (GAP). The enzyme that catalyzes this reaction is called aldolase (see).

In connection with the peculiarities of the enzyme systems participating in alcoholic fermentation, of the two named phosphotriosis, only GAF participates in further transformations, which should entail the loss for the fermentation process of half of the initial glucose molecule. However, this loss is prevented due to the presence in the cell of a specific enzyme - phosphotriose isomerase, which catalyzes a reversible reaction: dioxyacetone phosphate<->glyceraldehyde phosphate. This ensures that the entire sugar molecule can be used.

Oxidation of GAP is catalyzed by glyceraldehyde phosphate dehydrogenase (GAPDH) and results in the formation of an energy-rich compound, 1,3-diphosphoglycerate (1,3 DPG). The general reaction equation can be represented as follows:

The reaction proceeds in several stages: one of the SH groups of GAPDH participates in the addition of NAD + and the formation of a complex -

.

GAF is added to this complex, it is oxidized with the formation of an acyl enzyme:

Then hydrogen is transferred to NAD +:

and transport of acyl to the inorganic phosphate residue with the formation of 1,3-diphosphoglycerate:

The energy-rich bond of the phosphoric acid residue in the 1,3 DPG molecule enables the formation of ATP and 3-phosphoglycerol acid:

Intramolecular movement of the phosphate residue with the participation of phosphoglyceromutase leads to the formation of 2-phosphoglycerol to - you, which then turns into phosphoenolpyruvic to - that. With dephosphorylation of phosphoenolpyruvic to - you and its transformation into pyruvic to - that (pyruvate), the split off phosphate is transferred to ADP. The energy of the two ATP molecules formed at this stage is the net gain in energy that the cell acquires in the course of the entire complex chain of the processes described above. These processes are universal in nature and form the basis of not only alcohol, but also many other types of B., and primarily homofermentative lactic B., called glycolysis (see). It is very important to note that the listed reactions lead to the formation of pyruvate, which is used as a biol substrate, oxidation (see Biological oxidation) or respiration.

Under anaerobic conditions, pyruvate can be converted in different ways. Thus, in the case of alcoholic B., CO2 is cleaved from pyruvate with the participation of the decarboxylase enzyme and acetaldehyde is formed:

CH 3 -CO-COOH → CO 2 + CH 3 CHO.

With the participation of a specific enzyme (alcohol dehydrogenase), acetaldehyde is reduced to form the final product of alcoholic fermentation, ethyl alcohol. The hydrogen required for this reaction is obtained from the reduced coenzyme - nicotinamide adenine dinucleotide, or NAD-H. If in some way the reduction of acetaldehyde is prevented (for example, by binding it with sodium bisulfite), then hydrogen NAD-H, with the participation of the enzyme glycerophosphate dehydrogenase, can react with phosphotrioses and lead to the formation of glycerophosphate, and then glycerol.

One of the by-products of alcoholic fermentation is acetoin (acetylmethylcarbinol), CH 3 -CO-CHOH-CH 3, which is formed by the interaction of two molecules of pyruvic acid or pyruvic acid with acetaldehyde:

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

It is formed in the course of the so-called. karboligaznoy reaction, edges is catalyzed by enzymes isolated from yeast cells and from higher plants. Acetoin is also formed in other types of B. Acetoin is readily soluble in water, alcohol, ether. It is necessary to mention one more of the intermediate products of decomposition of carbohydrates in B., which is also a derivative of pyruvic acid. It is methylglyoxal (CH 3 COCHO), which chemically represents pyruvate aldehyde. When heated with water or when alkalizing aqueous solutions methylglyoxal turns into milk to - that. It can also be formed enzymatically - by the action of a specific enzyme methylglyoxylase. These compounds are formed in very small quantities.

Lactic acid fermentation

Lactic acid fermentation, which is very important, is genetically related to alcoholic fermentation. In this case, Pyruvic acid is not decarboxylated, as in alcoholic fermentation, but is directly reduced with the participation of specific lactate dehydrogenase due to NAD-H hydrogen.

Two groups are known lactic acid bacteria... The first of them includes homofermentative bacteria that form only milk to - that. Lactic acid bacteria of the second group (heterofermentative bacteria) form, in addition to lactic acid, also acetic acid, as well as ethyl alcohol (often in very significant quantities), carbon dioxide, formic to-that and some other products. The ratio between these products depends on many conditions (temperature, pH of the medium, etc.). This is often due to the joint activity of lactic acid bacteria with yeast. This kind of joint "leavens" are often created artificially and are widely used in bakery - when preparing rye bread, in the production of bread kvass and a number of lactic acid products (cheese, kefir, yogurt, koumiss, etc.). Lactic acid B. is widely used in the production of dairy to-you, which is used in a number of branches of the food, textile and leather industries.

Lactic acid bacteria are especially effective in thermophilic microbes of the Thermobacterium cereale type (formerly called Lactobacillus delbrukii). Formed milk to-that and as one of the products of the transformation of carbohydrates in the muscle tissue of animals in the process of glycolysis.

Butyric acid fermentation

Butyric acid fermentation is carried out in most cases by obligate anaerobes, that is, organisms that can exist only in an oxygen-free environment.

In the course of butyric acid fermentation, not only butyric acid are formed, but in some cases also very significant amounts of ethyl alcohol, lactic and acetic acids, and also gaseous hydrogen and carbon dioxide. Butyric acid decomposition of organic substances is carried out under conditions of a lack or complete absence of oxygen (swamps, wetlands). Butyric acid fermentation of pectin substances is of great industrial importance; At the same time, the activity of bacteria carrying out this type of B. must be prevented during the preparation of various kinds of food products in order to avoid deterioration of taste and deterioration of the latter (for example, rancidity of butter, silage, etc.).

Alcoholic, lactic and butyric B. - the main types of B.; the other numerous types of biology are either their various combinations, or are carried out on the basis of certain products arising in the course of the main type of biology. Thus, as a result acetic acid fermentation the oxidation of ethyl alcohol occurs with the participation of atmospheric oxygen. This type of B. is carried out by specific acetic acid bacteria. The total equation of acetic acid B.:

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

Upon exhaustion of alcohol reserves, bacteria oxidize the acetic acid formed by them to carbon dioxide and water.

B., carried out with the participation of O 2, includes gluconic acid fermentation- formation of gluconic acid from glucose:

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

It is caused by certain bacteria and molds. Gluconic acid is a valuable compound widely used in medicine and pharmaceutical industry (see. Gluconic acid).

Citric acid fermentation carried out by some representatives of molds; particular strains of Aspergillus niger are particularly effective. The initial product is Pyruvic acid, the transformation of a cut goes simultaneously in two directions. Part of it is oxidized into acetic acid, while the other, adding carbon dioxide, forms oxaloacetic acid. At condensation of acetic and oxaloacetic acids, citric acid is formed. In addition to citric acid, with citric acid B., butyl alcohol, acetone, and also ethyl alcohol, carbon dioxide, and hydrogen are formed.

Butanol-acetone fermentation carried out by the anaerobic bacteria Clostridium acetobutylicum. The main products formed in the course of this type of B. are n-butyl alcohol, acetone, ethyl alcohol, carbon dioxide, and hydrogen. Acetoacetic to - that (CH 3 COCH 2 COOH) and the acetone (CH 3 COCH 3) formed during its decarboxylation, as well as β-hydroxybutyric to - that make up the so-called group. acetone bodies (see. Ketone bodies), which accumulate in the blood and urine of animals in various pathological conditions and diseases (diabetes, starvation). Under normal conditions, these compounds are oxidized to form carbon dioxide and water harmless to the body.

High economic efficiency, the purity of valuable products obtained with biology underlie the ever wider use of biomass in the most varied sectors of the national economy.

Bibliography: Kretovich V.L. Fundamentals of plant biochemistry, M., 1971; Mahler G. and Yu. Cordes. Fundamentals of Biological Chemistry, trans. from English., M., 1970; Rubin B.A., Course of plant physiology, M., 1971; Racker E. Bioenergetic mechanisms, trans. from English, M., 1967. bibliogr .; Shaposhnikov V. N. Technical microbiology, M., 1948; H a s i d W. Z. Transformation of sugars in plants, Ann. Rev. plant Physiol., v. 18, p. 253, 1967, bibliogr.