How fermentation takes place. Method for inhibiting the growth of bacteria in alcoholic fermentation media
Fermentation- chemical reactions involving protein catalysts - enzymes. Usually occur in a living cell. Often confused with fermentation, fermentation is just the simpler part of the many complex fermentation processes. For example, as a result of fermentation, yeast reproduces, and under the action of enzymes produced by yeast, sugar is converted into alcohol.
Usage
Historically, the most ancient method of using fermentation is brewing. Grains of cereals contain insoluble hard-to-digest starch. This makes the grains protected against many bacteria for a very long time, but at the same time, starch is not available to the sprout itself. But a growing sprout produces enzymes that convert starch into easily soluble and digestible glucose. In brewing, grains are specially germinated and at the optimal moment of malt preparation, when the concentration of the enzyme is high, the germ is killed by heating. The enzyme continues to convert starch into sugar, which is used for further fermentation. Such an enzyme is amylase, which converts starch to maltose. Amylase is also found in saliva, due to which long-chewed rice or potatoes get a sweetish aftertaste.
Another ancient method of fermentation is cheese making. Various methods are used to coagulate milk.
Fermentation is a process of biochemical, very often oxygen-free decomposition of organic compounds, taking place with the participation of enzymes (enzymes). The end products of this process are simpler organic and inorganic compounds, as well as energy. Fermentation is a process reminiscent of breathing; for example, the metabolism of bacteria is based on it, it is the main means of obtaining the energy necessary for life in bacteria and various fungi adapted to living in the absence of oxygen. Fermentation is a type of fermentation in which enzymes are produced exclusively by microorganisms.
Fermentation types.
Microorganisms can ferment many different compounds, including sugars, fatty acids, and amino acids, and the process is slightly different in each case. The most common fermentation of sugars. As a result of fermentation, various products are formed - for example, alcohols or lactic acid - therefore, in particular, alcoholic, acetic, butyric and lactic fermentations are distinguished.
How does this happen?
As a result of the fermentation of sugars, simple (glucose, fructose) or complex (maltose, sucrose, lactose) sugars decompose to ethyl alcohol and carbon monoxide. The process takes place with the participation of yeast, more precisely zymase (a group of enzymes secreted by yeast). In addition to alcoholic fermentation, lactic acid fermentation is very common, as a result of which lactic acid is formed. During acetic fermentation, in turn, alcohols are oxidized to acetic acid, however, it does not involve yeast, but special bacteria (of the Acetobacter family). In the process of fermentation, other products are formed, but in all cases, energy is released.
The use of fermentation and fermentation.
The phenomenon of fermentation is widely used in the food, wine, brewing and alcohol industries. Wine fermentation - that is, the fermentation of sugars contained in grapes and other fruits - is used to make wine. The fermentation properties of yeast have been used in baking, as the carbon dioxide (carbon dioxide) produced by them makes the dough “fit”. Acetic fermentation is used in the production of vinegar. Fermentation of proteins is widespread in nature, contributing to the decomposition of organic residues; Butyric fermentation is used industrially to produce butyric acid. Lactic acid fermentation is used, for example, for the production of lactic acid products and pickling vegetables. In addition, lactic acid is used in the leather and dye industry.
Do you know that:
- Thanks to lactic acid fermentation, we have kefir.
- Biologists consider fermentation to be the oldest type of metabolism (metabolism). It is likely that the first organisms received energy using this particular process - after all, at that time there was no oxygen in the earth's atmosphere.
- Pickles are also a product of fermentation processes.
- When the muscles work, they also undergo a fermentation process - the decomposition of glucose with the release of energy, at the intermediate stage of which lactic acid is formed. In the event of a lack of oxygen, lactic acid does not decompose, but accumulates in the muscles, irritating the nerve endings and causing a person to feel tired.
- The phenomenon of alcoholic fermentation is used in the food industry. Wines are made from fermented grapes (or other berries and fruits).
Usage: microbiological and food industry. Essence of the invention: A method for inhibiting the growth of bacteria in alcoholic fermentation media is carried out by adding a polyester ionophore antibiotic to the fermentation medium at a concentration of 0.3-3.0 ppm. 2 s.p.f-ly, 2 tables, 2 ill.
The invention relates to a method for inhibiting the growth of bacteria in alcoholic fermentation media. It is known that alcoholic fermentation plants do not operate under sterile conditions and therefore can contain bacterial populations that reach concentrations of 10 4 to 10 6 microorganisms/ml, and in extreme cases even more. These microorganisms may belong to the lactobacillus family, but may also include other types of microorganisms such as streptococcus, bacillus, pediococcus, clostridium, or leuconostoc (see Table 1). All these bacteria have the ability to form organic acids. If the concentration of bacteria in the population exceeds 10 6 microorganisms/ml, the formation of organic acids can reach a significant level. At concentrations above 1 g/l, such organic acids can interfere with the growth and fermentation of yeast and lead to a decrease in plant productivity by 10-20% or more. In some raw materials, such as wine, cider, or their products, such bacteria can also convert glycerol to acrolein, which is a carcinogenic compound found in the final alcohol product for human consumption. Thus, in order to prevent the negative effects caused by the overgrowth of bacteria in the fermentation medium, bacteriostatic and/or bactericidal methods are needed that do not adversely affect the fermentation process. It is known to use antibiotics for this purpose, such as penicillin, lactocide, nisin, which are introduced into fermentation media, in particular from molasses, starch and grain in the production of alcohol (1). The disadvantage of such methods lies either in the low activity of the antibiotic, or in the fact that some antibiotics (penicillin) lead to the formation of mutant strains that are resistant to the action of the antibiotic. The objective of the invention is to eliminate these shortcomings. This problem is solved using the proposed method, according to which a polyester ionophore antibiotic of a bacteriostatic or bactericidal agent is introduced into the fermentation medium. The process of the present invention can be used with a wide variety of fermentation media, including sugar beet juice, sugar cane juice, dilute sugar beet molasses, diluted sugar cane molasses, hydrolyzate of cereals (e.g., corn or wheat), hydrolyzate of starch tubers ( such as potatoes or Jerusalem artichoke), wine, wine by-products, cider, as well as its by-products. Therefore, any starch- or sugar-containing materials that can be fermented with yeast to produce alcohol (ethanol) can be used in accordance with the present invention. The resulting bacterial control or greatly reduces the problems caused by the presence of bacteria and the organic acids they produce. The polyester ionophores that can be used in the present invention do not adversely affect the yeast (saccharomices sp.) and the fermentation process. Polyether ionophore antibiotics that can be used in the present invention are any antibiotics that do not significantly affect yeast and that have a bacteriostatic and/or bactericidal effect on organic acid producing bacteria in the fermentation medium. Most useful in the present invention are antibiotics that are effective against the bacteria listed in table. 1 (see above). Preferred polyester ionophore antibiotics are monensin, lazalozide, salinomycin, narasin, maduramycin and semduramycin. More preferred are monensin, lazalozide and salinomycin, however, the most preferred antibiotic is monensin. Fermentation media that can be effectively processed by the method of the present invention include raw materials such as, for example, sugar beet juice, sugar cane juice, dilute sugar beet molasses, dilute sugar cane molasses, hydrolyzate of cereals (for example, corn or wheat), hydrolyzate of starch tubers (eg potato or Jerusalem artichoke), wine, winemaking by-products, cider and by-products of its production. Therefore, any starch- or sugar-containing materials that can be fermented with yeast to produce alcohol (ethanol) can be used in accordance with the present invention. Polyether ionophore antibiotics are highly stable compounds. They do not readily decompose over time or at high temperatures. This is important for fermentation plants because: 1. they remain active for many days under normal operating conditions of the fermentation plant; 2. they remain active at the high temperatures that occur during enzymatic hydrolysis prior to cereal or tuber fermentation (eg 2 hours at 90° C. or 1.5 hours at 100° C.). These compounds are commercially available and supplied by pharmaceutical companies. Experiments were carried out with various polyester ionophore antibiotics such as monensin, lazalozide and salinomycin using sugar beet molasses based fermentation feedstock. Experiments performed have confirmed the existence of bacteriostatic or bactericidal concentrations that lie in the range of about 0.5 to 1.5 ppm. Under bacteriostatic conditions, the growth of the bacterial population stops and it can be found that the content of organic acids in the population does not increase. At bactericidal concentrations, the bacterial population decreases and therefore the concentration of organic acids does not increase. According to the method of the present invention, a bacteriostatic or bactericidally effective amount of at least one polyester ionophore antibiotic is introduced into the fermentation medium. Preferably, at least one polyester ionophore antibiotic is added to the fermentation medium at a concentration of about 0.3 to 3 ppm. Most preferably, the concentration of the polyester ionophore antibiotic is from about 0.5 to 1.5 ppm. The polyester ionophore according to the invention prevents or inhibits the growth of bacteria in the fermentation medium without affecting the yeast at concentrations up to 100 ppm. The bacterial flora can be maintained at a concentration of 10 4 microorganisms/ml and below, which leads to almost complete cessation of the formation of organic acids. Therefore, bacteria cannot significantly reduce alcoholic fermentation. Under these conditions, bacteria usually do not contribute to the formation of acrolein. At concentrations of about 0.5 ppm, the antibiotic has a bactericidal effect and therefore makes it possible to achieve a reduced bacterial count. In FIG. 1 shows the reduction in bacterial population in diluted molasses after the addition of monensin; in fig. 2 - the effect of monensin on the population of bacteria in a continuous fermentation process in an industrial plant. Example 1 Effect of monensin on the concentration of Lachobacillus buchneri. Various concentrations of monensin are added to dilute sugar beet molasses and the acidity and concentration of microorganisms are measured. The results obtained are presented in table. 2. Example 2 Stability and bactericidal action of monensin in molasses juice. A dilute molasses juice containing 10 6 microorganisms/ml is injected with monensin at a concentration of 1 ppm. Figure 1 shows the decrease in the bacterial population after 20 days at a temperature of 33 o C. Resumption of bacterial growth was observed. These data show that monensin remains active for 20 days at 33° C. under normal operating conditions of the fermentation unit. Example 3 Industrial use of monensin. Another example of the present invention is shown in Fig.2. It refers to an alcoholic fermentation plant that operates continuously. The fermentation medium is molasses containing 14% sugar (about 300 g/l). The flow rate is 40-50 m 3 /h, the temperature is 33 o C. On the 7th day, the contamination with microorganisms exceeds 10 6 microorganisms/ml. On the 8th day, treatment is started by introducing an active amount of monensin (dissolved in ethanol) into the fermenter. This concentration of monensin is maintained for 24 hours by introducing an enrichment feed containing monensin at the same concentration. On day 9, the addition of monensin to the raw material is stopped. Immediately after the start of treatment, the bacterial population begins to decrease rapidly. This decrease continues until the 10th day, that is, within 24 hours after the end of the treatment. At this stage, monensin is washed out of the fermentation medium and bacterial growth slowly resumes. It is controllable over the next 15 days, however, this is due to the reduced level of contamination after treatment.
Claim
1. A method for inhibiting the growth of bacteria in alcoholic fermentation media by adding an antibiotic to the fermentation medium, characterized in that a polyester ionophore antibiotic is used as an antibiotic. 2. The method according to claim 1, characterized in that the polyester ionophore antibiotic is added to the fermentation medium at a concentration of 0.3 to 3.0 ppm. 3. The method according to claim 1, characterized in that the antibiotic is added to a fermentation medium based on juice or molasses of sugar beet or sugar cane, or starch hydrolyzate from cereals or tubers, or wine-making or cider-making media.
tea making process is a sequence of interrelated steps, at the very beginning of which is a freshly picked leaf, and at the very end is what we in the trade call "finished" or "ready" tea. The six types of tea (green, yellow, white, oolong, black, and pu-erh) have several similar processing steps (such as picking, primary sorting, finishing, etc.), but also have nuances that are unique to one or several specially prepared teas. Oxidation is one of the most recently described chemical processes that must occur in the manufacture of some types of teas, and must be prevented in the manufacture of others. We can say that all types of tea are divided into two large classes, depending on whether oxidation is involved in obtaining the finished product or not.
Oxidation in tea
First, let's define oxidation. Oxidation- This is a biochemical, enzymatic process during which oxygen is absorbed and (as a result) changes in the substances involved in the process occur. In the case of freshly picked tea leaves, tea - the substances contained in the tea leaves. Oxidation can be spontaneous or controlled and lead to both positive and negative changes. A well-known example of spontaneous negative oxidation is what happens when you cut open an apple or banana, or leave a cut piece of leaf out in the open. Unprotected cells absorb oxygen, soften, and turn brown. This is the simplest form of oxidation that most people are familiar with. If the oxidation process is not interfered with, then the fruit may simply dry out or rot, depending on atmospheric conditions. By simply cutting an apple into pieces and drying them in a dehydrator (desiccant), one can observe an example of controlled negative oxidation occurring during the drying process. Darkening of the cut surface is not considered aesthetically pleasing in the market, so discoloration is sometimes corrected with sulfur compounds or citric acid, but even in this situation (no visible color change) oxidation still occurs.
During tea production, both spontaneous and controlled oxidation is present. Spontaneous oxidation occurs during the drying stage of the tea leaf in the manufacture of white, oolong and black teas. The controlled oxidation stage, which requires special attention, is one of the most important stages in the production of both oolong and black teas. In green and yellow teas, oxidation is prevented by careful steaming, drying and/or roasting, which is also often referred to as "de-enzyming".
Oxidation is a chemical process that requires an excess of moist, oxygen-rich air. In the production of black tea in oxidation rooms, 15 to 20 exchanges of humidified air per hour must be performed to ensure complete oxidation. The polyphenols in the leaf (tea catechins) take up significant amounts of oxygen, especially during the early stages of oxidation. Oxidation in tea production formally begins spontaneously from the moment the tea leaf is dried, and is then gradually accelerated by subsequent steps necessary to turn the fresh leaf into finished black tea. After several preparatory steps, the pre-prepared sheet is ready for the controlled oxidation process, which is often erroneously referred to as "fermentation". In traditional oxidation, sorted sheet is spread in thin layers (maximum 5 to 8 cm) on the floor of the factory, on tables, on porous pallets - and this is similar to drying, which is done at the stage of primary drying. Oxygenation of polyphenols begins a series of chemical reactions involving them, eventually producing new aromatic components and providing a more "dense" infusion characteristic of black tea. During the first and most important period of enzymatic oxidation, the polyphenol oxidase and peroxidase (a group of redox enzymes that use hydrogen peroxide as an electron acceptor) attack other polyphenols, resulting in theaflavins. These red-orange compounds further act on polyphenols to produce thearubigins, which are also chemically responsible for changing leaf color from green to gold, copper, chocolate brown. Thearubigins, meanwhile, interact with several amino acids and sugars in the leaf to create highly polymeric substances that develop into the diverse and distinctive flavor components we expect black tea to have.
Basically, theaflavins bring freshness and brightness to the taste of black tea, while thearubigins determine its strength, richness and color.
In the process of oxidation, carbon dioxide is released from the tea leaf and the temperature of the mass of oxidized leaves rises. If the leaf temperature is allowed to rise too high, oxidation will get out of control; if the temperature falls too low, the oxidation will stop.
An array of tea leaves in the process of controlled oxidation is called "dhool" (dhool). Oxidation requires 2 to 4 hours and can be controlled empirically, not scientifically. Although there may be technical markers for determining the expected completion of a process, there are also many parameters that characterize the process and are observed "live". Therefore, the best method for determining the moment of complete leaf oxidation may be expert visual and olfactory observation.
The tea master must control the thickness and uniformity of the layer of leaves, make sure that the temperature is about 29 C, the relative humidity is 98%; and provide constant ventilation (15 or 20 complete room air changes per hour). Also, the microclimate must be completely hygienic; bacteria can ruin dhul.
When in the process of oxidation, the processed leaf (dhul) receives a predictable series of taste parameters, a fresh, rich color and a final strength. The tea master can control the oxidization of the dhula in his own particular way, adjusting the duration of the oxidization, allowing the oxidization to be combined with changes in temperature/humidity in the oxidizing room. Most of the teas produced produce a balanced infusion in the cup with bright infusion, good intense aroma, and a thick, rich body. When the tea master determines that the dhul has oxidized to the desired level (“fully oxidized” is a degree, not absolute), then the critical phase of controlled oxidation is stopped by the final process of black tea production: drying.
fermentation in tea
Fermentation It is an important ingredient in the production of pu-erh and other aged teas such as Luan, Liubao, some oolong teas, etc. It is most convenient to talk about fermentation in tea production using the example of the production of pu-erh. Let's explore what fermentation is and why careful and skillful fermentation is inseparable from the production of traditional, high-quality pu-erhs. Despite the fact that the production of pu-erh is one of the oldest and simplest forms of tea production, the world of pu-erh is so complex and vast that it has become the subject of close attention of tea experts and requires special care in studying. In any case, we will not explore the specific complexity of producing different types of pu-erh here, as this article only proposes to consider the more basic description of fermentation and oxidation.
Fermentation is a microbial activity (activity) involving certain types of bacteria. By definition, fermentation occurs most easily in the absence of oxygen, although some environmental exposure is ideal for aging unripe sheng puerh. While an abundance of oxygen is required for most steps in tea making, exposure to oxygen in pu-erh production is often reduced or eliminated after the tea leaf drying step. The leaf that transforms into pu-erh must be exposed to bacteria (or has bacteria by its nature) suitable for fermentation.
As in the case of the production of “fermented” apple cider or Roquefort cheese, the bacteria necessary for the activity of microorganisms begin to naturally reproduce outdoors and / or inside a special fermentation room (cider “house” or cheese ripening chamber). In the case of pu-erh, the bacteria required to both initiate and maintain fermentation are found in the following locations.
- On the surface of the leaf itself from old trees in a primeval forest where large-leaved trees grow - the most famous of them in the Xishuangbanna region in the southwest of Yunnan province in China.
- In a climate-controlled tea production facility in which "raw (sheng) mao cha" is temporarily stockpiled while awaiting pressing; in heaps of “mao-cha” during artificial fermentation of finished (shu) pu-erh; or in humid, steamy climates where pu-erh is pressed.
- In dry cool rooms where sheng pu-erh pancakes are stored for post-fermentation and aging under careful control.
During the fermentation phase in the production of pu-erh, several important factors must come together. During the harvest, on the leaf itself, which meets the standards, there must be “wild” bacteria - there may be very many or very few of them, and the quality of the tea will also depend on this. The leaf destined to become pu-erh ("maocha" dried-withered, roasted to "kill the greens" (sa cheen, shaqing), crushed (ro nien, rounyan), and then the partially dried leaf) is put into bags and place these bags on top of each other in anticipation of pressing in bacteria-saturated steam; or, in the case of ready-made shu pu-erh, it is piled in heaps indoors, exposed to external influences. Unlike the low, porous piles of leaves harvested for oxidation, the piles of mao cha in which artificial fermentation of shu pu'er is stimulated are stacked tightly, compactly, and with minimal exposed surface area. The pile of maocha is stirred infrequently - to give the leaves a "rest" (and prevent fermentation from going too far), supply the bacteria with the oxygen they need, and provide the temperature desired for favorable microbial growth and desired leaf transformation. During the fermentation of pu-erh, heaps are often covered - in order to increase the temperature of the processes occurring in the leaves.
One can imagine the slight confusion that leads tea merchants to observe the processes of drying, oxidation and fermentation. Observing the mixing of leaf piles on the floor, piles of leaves in trenches or on decks, novice tea merchants may be dumbfounded by the fact that the processes that take place in the production of tea are rudimentary and artisanal (this artisanality is exacerbated by the Chinese reluctance to explain their "secrets"). And, although a lot has been described over the past 75 years, it is still difficult to clearly separate the processes of drying, fermentation and oxidation (and, accordingly, to clearly manage them).
It is imperative that both consumers and tea merchants are aware of the characteristic differences between oxidation and fermentation. These processes should be clear and not get lost in tea terminology or marketing gimmicks.
A good sign that distinguishes a good trader is his understanding of the essence of the production of white, oolong and black teas, which are very dependent on drying and oxidation processes. The use of the terms "oxidation" and "fermentation" inappropriately contributes to confusion among tea drinkers. In addition, those who can correctly identify what type of pu-erh is offered for purchase, and what conditions are necessary for the complete completion of unripe sheng pu-erh in its maximum development (long aging, aging, and aging), provide themselves with a reliable purchasing base. For tea enthusiasts, knowledge is power, the tea world is becoming more and more accessible, and knowledge guarantees us more and more quality tea, and many other joyful moments of real pleasure from drinking your favorite drink.
(More information about tea production and an explanation of the oxidative processes in different types of tea can be found in The Tea Story; A Cultural History and Drinking Guide by Mary Lou Heiss and Robert J. Heiss, Ten Speed Press October 2007)
| Green tea | No oxidation * |
| yellow tea | No oxidation * |
| White tea | Light spontaneous oxidation (8-15%) |
| Oolong tea | Production-controlled partial oxidation (level 15-80%) |
| Black tea | Full oxidation, controlled during production |
| Puer | Fully fermented, not fully oxidized, there are two main directions |
| sheng pu-erh | Raw, original, or "green" pu-erh - uncontrolled oxidation, although minimal spontaneous oxidation may be present |
| Shu pu-erh | Ready, mature, or "black" pu-erh - controlled oxidation as essential to the "accelerated aging" process |
* The wording "No oxidation" should be understood as "Almost no oxidation". This is a translator's note.
50. Metabolism of bacteria. Fermentation. Types of fermentation. Microorganisms that cause these processes
Metabolism is a set of various enzymatic reactions that occur in a microbial cell and are aimed at obtaining energy and converting simple chemical compounds into more complex ones. Metabolism ensures the reproduction of all cellular material, including two single and simultaneously opposite processes - constructive and energy metabolism.
Metabolism proceeds in three stages:
1. catabolism - the breakdown of organic substances into simpler fragments;
2. amphibolism - intermediate exchange reactions, as a result of which simple substances are converted into a number of organic acids, phosphoric esters, etc .;
3.anabolism - the stage of synthesis of monomers and polymers in the cell.
Metabolic pathways were formed in the process of evolution.
The main property of bacterial metabolism is plasticity and high intensity due to the small size of organisms.
Metabolic pathways in prokaryotes include fermentation, photosynthesis, and chemosynthesis. The most primitive way of obtaining energy, inherent in certain groups of prokaryotes, are fermentation processes.
Fermentation- a metabolic process inherent in bacteria, characterizing the energy side of the mode of existence of several groups of prokaryotes, in which they carry out redox transformations of organic compounds under anaerobic conditions, accompanied by the release of energy that these organisms use.
fermentation proceeds without the participation of molecular oxygen, all redox transformations of the substrate occur due to its "internal" capabilities. As a result, at the oxidative stages of the process, a part of the free energy contained in the substrate molecule is released, and it is stored in ATP molecules. There is a splitting of the carbon skeleton of the substrate molecule.
The range of organic compounds that can be fermented is quite wide:
Carbohydrates, alcohols, organic acids, amino acids, purines, pyrimidines.
Can be fermented if it contains incompletely oxidized (or reduced) carbon atoms
fermentation products are various organic acids (lactic, butyric, acetic, formic), alcohols (ethyl, butyl, propyl), acetone, as well as CO2 and H2
several products are formed. Depending on which main product accumulates in the medium, lactic acid, alcohol, butyric, propionic and other types of fermentation are distinguished.
In each type of fermentation, two sides can be distinguished: oxidative and reductive. Oxidation processes are reduced to the detachment of electrons from certain metabolites with the help of specific enzymes (dehydrogenases) and their acceptance by other molecules formed from the fermented substrate, i.e., anaerobic type oxidation occurs during fermentation
The energy side of the fermentation processes is their oxidative part, the reactions are oxidative
There are several exceptions to this rule: some anaerobes also receive part of the energy during the fermentation of the substrate as a result of its splitting catalyzed by lyases.
The primitiveness of fermentation processes lies in the fact that only a small fraction of the chemical energy that it contains is extracted from the substrate as a result of its anaerobic transformation. The products formed during the fermentation process still contain a significant amount of energy contained in the original substrate.
During respiratory metabolism, 2870.22 kJ / mol of energy is released during the breakdown of glucose, and 196.65 kJ / mol of energy is extracted during fermentation on the same substrate. In the process of homofermentative lactic acid fermentation, 2 ATP molecules are synthesized per 1 molecule of fermented glucose; in the process of respiration, with the complete oxidation of a glucose molecule, 38 ATP molecules are formed. In both cases, the efficiency of storage of the released energy in macroergic bonds of ATP is approximately the same.
During fermentation, some reactions in the pathway of anaerobic substrate conversion are associated with the most primitive type of phosphorylation, substrate phosphorylation, whose reactions are localized in the cytosol of the cell, which indicates the simplicity of the chemical mechanisms underlying this type of energy production.
* Alcoholic fermentation. During alcoholic fermentation from pyruvic acid, as a result of its oxidative decarboxylation, acetaldehyde is formed, which becomes the final hydrogen acceptor. As a result, 2 molecules of ethyl alcohol and 2 molecules of carbon dioxide are formed from 1 molecule of hexose. Alcoholic fermentation is common among prokaryotic (various obligate and facultative anaerobic bacteria) and eukaryotic (yeast) forms.
The ability to carry out alcoholic fermentation under anaerobic conditions: Sarcina ventriculi, Erwinia amylouora, Zymomonas mobilis. The main producers of ethyl alcohol among eukaryotes are aerobic yeasts with a formed respiratory apparatus, but under anaerobic conditions they carry out alcoholic fermentation along the path of substrate phosphorylation.
* Lactic acid fermentation is homofermentative, in which up to 90% of lactic acid is formed among the products, and heterofermentative, in which, in addition to lactic acid, CO2, ethanol and / or acetic acid make up a significant proportion in the products.
a) Lactic acid fermentation (homofermentative) is the process of obtaining energy by lactic acid bacteria Lactococcus lactis, Lactobacterium bulgaricum, Lactobacterium planterum, etc., which consists in the conversion of a sugar molecule into two molecules of lactic acid with the release of energy: C6H12O6 \u003d 2CH3CHOHCOOH + 0.075x106 J
b) Lactic acid fermentation (heterofermentative). In this process, in addition to lactic acid, acetic acid, succinic acid, ethyl alcohol, carbon dioxide and hydrogen are formed among the products. The causative agent of this process is E. coli.
A process similar to atypical heterofermentative lactic acid fermentation occurs during the maturation of spicy salted fish and preserves. In these cases, it is excited by aroma-forming lactic acid bacteria such as Streptococcus citrovorus.
In addition, with spoilage of canned food caused by bacteria you. stearothermophilus and Cl. thermosaccharolyticum, acids accumulate in the product - lactic, acetic, butyric, the formation of which is probably associated with a process similar to atypical lactic acid fermentation.
*Butyric fermentation is caused by obligately anaerobic butyric bacteria Cl. pasteurianum. Glucose in this energy-giving process turns into butyric acid, hydrogen and carbon dioxide: C6H12O6 \u003d C3H7COOH + 2CO2 + 2H2 + 0.063x106 J
Some clostridia, such as Cl. sporogenes or toxic species Cl. botulinum, Cl. perfringens have proteolytic abilities and not only ferment carbohydrates, but also hydrolyze proteins. The causative agents of butyric fermentation form heat-resistant spores, so they can persist in sterilized canned food and cause bombing spoilage.
Many other fermentations are known, some types of which differ in the composition of the final products, which depends on the enzyme complex of the fermentation agent.
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