Glucose fermentation is one of the main reactions by which the preparation of alcoholic beverages is possible. It can be carried out in different ways, in each of which individual products are formed. This process plays a key role in many areas of our life, from cooking and making wine and vodka products to the reactions that take place in our body.
History
The process of fermentation of glucose and other sugars was used by ancient people. They ate slightly fermented food. Such food was safer, as it contained alcohol, in which many harmful bacteria died. In ancient Egypt and Babylon, people already knew how to ferment many sugary drinks and milk. When people at the end of the 18th century managed to better study this process, its types and possibilities for improvement, such industries as kvass, brewing and wine-vodka grew very qualitatively.
Types of fermentation
Oddly enough, but this process is different. And there are types of glucose fermentation by end products. Thus, there is lactic acid, alcohol, citric acid, acetone, butyric and several others. Let's talk a little about each type ofseparately. Lactic acid fermentation of glucose is the main process in the preparation of such products as yogurt, sour cream, kefir, cottage cheese. It is also used to preserve vegetables and performs a key function in our body: in conditions of lack of oxygen, glucose is converted into the final product - lactic acid, which causes muscle pain during and after training.
Alcoholic fermentation is different in that ethyl alcohol is formed as the final product. It occurs with the help of microorganisms - yeast. And it plays a key role in cooking, since in addition to the main product, carbon dioxide is released during the alcoholic fermentation of glucose (this explains the splendor of the yeast dough).
Citric acid fermentation occurs, as you might guess, with the formation of citric acid. It occurs under the influence of a certain type of fungus and is part of the Krebs cycle, which ensures the respiration of all cells in our body.
Acetone-butyl fermentation is very similar to butyric fermentation. As a result, butyric acid, butyl and ethyl alcohols, acetone and carbon dioxide are formed. Butyric fermentation produces only the name-bearing acid and carbon dioxide.
Now we will look at all types in more detail, but let's start with the most basic - alcoholic fermentation of glucose. All reactions and the nuances of their course will be analyzed in detail.
Alcohol fermentation
Let's tell a little more about the fermentation of glucose, the equation of which is:S6N12O6 =2S2N 5OH + 2CO2. What can be learned from this reaction? We have two products: ethyl alcohol and carbon dioxide. Due to the latter, we observe the swelling of the yeast dough. And due to the first, we have the opportunity to get an unforgettable taste of wine and wine drinks. But in fact, this is just a simplified equation. The complete glucose fermentation reaction is more complicated, so let's break it down a bit.
There is such a process as glycolysis. Literally, its name translates as "splitting of sugar." It occurs in the body, and its by-product is pyruvic acid, and the main one is adenosine triphosphate (ATP), which is formed during this reaction from another compound. We can say that ATP is the energy carrier in the body, and in fact, glycolysis serves to provide our body with energy.
We touched on this process for a reason. In fact, fermentation is very similar to glycolysis, since the first stage is exactly the same for them. It can even be said that the alcoholic fermentation of glucose is a continuation of glycolysis. The pyruvate (pyruvic acid ion) formed in the course of the latter is converted into acetaldehyde (CH3-C(O)H) with the release of carbon dioxide as a by-product. After that, the resulting product is reduced by the NADH coenzyme contained in the bacteria. Reduction leads to the formation of ethyl alcohol.
Thus, the fermentation reaction of glucose to ethyl alcohol looks like this:
1)C6H12O6=2 C3H 4O3 + 4 H+
2) C3H4O3=CH3 -COH + CO2
3) CH3-COH + NADH + H+=C2H 5OH + NAD+
NADH serves as a catalyst for the reaction, and the NAD ion+plays a key role in the early stage of glycolysis, and, formed at the end of alcoholic fermentation, returns to the process.
Let's move on to the next type of reaction under study.
Lactic acid fermentation of glucose
This species differs from alcohol in that it occurs not under the influence of yeast, but with the help of lactic acid bacteria. Therefore, we have completely different products. Lactic acid fermentation also occurs in our muscles under high stress and lack of oxygen.
There are two types of this process. The first is homofermentative fermentation. If you have ever heard the prefix "homo", then you probably understand what it means. Homofermentative fermentation is a process involving a single enzyme. At the first stage, glycolysis occurs and pyruvic acid is formed. Then the resulting pyruvate (in solution this acid can exist only in the form of ions) is subjected to hydrogenation using NADH+H and lactate dehydrogenase. As a result, the reduction product is lactic acid, which makes up about 90% of all products obtained during the reaction. This compound, however, can also be formed in the form of twodifferent isomers: D and L. These types differ in that they are mirror images of each other and, as a result, affect our body in different ways. Which isomer will be formed to a greater extent determines the structure of lactate dehydrogenase.
Let's move on to the second type of lactic acid fermentation - heterofermentative. This process involves several enzymes and follows a more complex path. Because of this, more different products are formed during the reaction: in addition to lactic acid, we can find acetic acid and ethyl alcohol there.
So we have considered lactic acid fermentation. This is the process by which we can enjoy the taste of cottage cheese, curdled milk, fermented baked milk and kefir. Let's sum up and write down the general reaction of lactic acid fermentation of glucose: C6H12O6=2 C 3H6O3. Of course, this is a simplified diagram of the process of homofermentative fermentation, since even the diagram of a heterofermentative fermentation process will be very complex. Chemists are still studying the lactic fermentation of glucose and elucidating its full mechanisms, so there is still room for improvement.
Citric acid fermentation
Reactions of this type of fermentation occur, as with alcohol, under the action of mushrooms of a certain strain. The full mechanism of this reaction is not yet fully understood, and we can only rely on some simplifications. However, there are suggestions that the initial stage of the process is glycolysis. Then pyruvic acid is converted toturns into various acids and comes to citric. Due to this mechanism, other acids accumulate in the reaction medium - products of incomplete oxidation of glucose.
This process occurs under the influence of oxygen, and in general terms it can be written as the following equation: 6 +3O2=2C6N8O 7 + 4H2O. Before this type of fermentation was discovered, people extracted citric acid exclusively by pressing the fruit of the corresponding tree. However, this acid is not more than 15% in lemon, so this method turned out to be impractical, and after the discovery of this reaction, all the acid began to be obtained by fermentation.
Butyric fermentation
Let's move on to the next type. This type of fermentation occurs under the action of butyric acid bacteria. They are widespread, and the process they cause plays a key role in biologically important cycles. With the help of these bacteria, the decomposition of dead organisms occurs. The butyric acid formed during the reactions attracts scavengers with its smell.
This type of fermentation is used in industry. As you might guess, they get butyric acid. Its esters are widely used in perfumery and have a pleasant smell, unlike itself. However, butyric fermentation is not always beneficial. It can spoil vegetables, canned food, milk and other products. But this can happen only if butyric acid bacteria have entered the product.
Let's analyze the mechanism of butyricfermentation of glucose. His reaction looks like this: C6H12O6 → CH3 CH2CH2COOH + 2CO2↑ + 2H2 . As a result, energy is also generated, which ensures the vital activity of butyric bacteria.
Acetone-butyl fermentation
This type is very similar to butyric. Not only glucose, but also glycerol and pyruvic acid can ferment in this way. This process can be divided into two stages: the first (sometimes called acidic) is actually butyric fermentation. However, in addition to butyric acid, acetic acid is also released. As a result of glucose fermentation in this way, we get products that go to the second stage (acetonobutyl). Since this whole process also occurs under the action of bacteria, when the medium is acidified (increase in the concentration of acids), special enzymes are released by bacteria. They induce the conversion of glucose fermentation products into n-butanol (butyl alcohol) and acetone. In addition, some ethanol may be produced.
Other types of fermentation
In addition to the five types of this process listed, there are several more. For example, this is acetic fermentation. It also occurs under the action of many bacteria. This type of fermentation can be used for useful purposes when pickling. It protects food from pathogenic and dangerous bacteria. There are also alkaline or methane fermentation. Unlike the previous types, this typefermentation can be carried out for most organic compounds. As a result of a large number of complex reactions, organic substances are split into methane, hydrogen and carbon dioxide.
Biological role
Fermentation is the most ancient way of obtaining energy by living organisms. Some creatures produce organic substances, receiving energy along the way, while others destroy these substances, while also receiving energy. Our whole life is built on this. And in each of us, fermentation takes place in one form or another. As we said above, lactic acid fermentation occurs in the muscles during intense training.
What else to read?
If you are interested in the biochemistry of this very interesting process, you should start with school textbooks in chemistry and biology. Many university textbooks are so detailed that after reading them you can become just an expert in this field.
Conclusion
Here we come to the end. We analyzed all types of glucose fermentation and the general principles of these processes, which play a very important role both in the functioning of living organisms and in our industry. It is possible that in the future we will discover several more types of this ancient process and learn how to use them to our advantage, as we did with those already known to us.
