Glucose fermentation is one of the main reactions with 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 sectors of our lives, from cooking and the preparation of 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 a little fermented food. Such food was safer because it contained alcohol, in the environment of which many harmful bacteria died. In ancient Egypt and Babylon, people already knew how to ferment many sugar-containing drinks and milk. When people at the end of the 18th century managed to better study this process, its types and opportunities for improvement, such industries as kvass, brewing and wine and vodka grew very qualitatively.
Types of fermentation
Oddly enough, but this process is different. And they distinguish between types of glucose fermentation in the final products. Thus, there is lactic acid, alcoholic, citric acid, acetone, butyric acid and several others. Let's talk a little about each species separately. Lactic acid fermentation of glucose is the main process in the preparation of products such as yogurt, sour cream, kefir, cottage cheese. It is also used to preserve vegetables and performs a key function in our body: in the absence of oxygen, glucose turns into the final product - lactic acid, which causes muscle pain at the time of training and a little after it.
Alcoholic fermentation is characterized 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 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 mushroom 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 acid. As a result, butyric acid, butyl and ethyl alcohols, acetone and carbon dioxide are formed. With oily fermentation, only the acid and carbon dioxide corresponding to the name are formed.
Now we will consider all types in more detail, but we will begin with the most basic - alcoholic fermentation of glucose. All reactions and the nuances of their course will be analyzed in detail.
Alcohol fermentation
We will tell a little more about the fermentation of glucose, the equation of which is: C 6 H 12 O 6 = 2C 2 H 5 OH + 2CO 2 . What can be learned from this reaction? We have two products: ethyl alcohol and carbon dioxide. Due to the latter, we observe a 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 only a simplified equation. The complete glucose fermentation reaction is more complicated, so let's take it a little deeper.
There is a process like glycolysis. Literally, its name translates as "sugar breakdown." It occurs in the body, and its by-product is pyruvic acid, and the main one is adenosine triphosphoric acid (ATP), which is formed during this reaction from another compound. We can say that ATP is a carrier of energy in the body, and in fact glycolysis serves to provide our body with energy.
We knowingly touched this process. In fact, fermentation is very similar to glycolysis, since the first stage is exactly the same for them. You can even say that the reaction of alcoholic fermentation of glucose is a continuation of glycolysis. Pyruvate (pyruvic acid ion) formed during the latter is converted to acetaldehyde (CH 3 -C (O) H) with the release of carbon dioxide as a by-product. After that, the resulting product is restored by the coenzyme NADH contained in bacteria. Recovery leads to the formation of ethyl alcohol.
Thus, the reaction of glucose fermentation to ethanol looks like this:
1) C 6 H 12 O 6 = 2 C 3 H 4 O 3 + 4 H +
2) C 3 H 4 O 3 = CH 3 —COH + CO 2
3) CH 3 -COH + NADH + H + = C 2 H 5 OH + NAD +
NADH serves as a catalyst for the reaction, and the NAD + ion plays a key role in the early stages of glycolysis, and, formed at the end of alcoholic fermentation, returns to the process.
Let's move on to the next variety of the investigated type of reactions.
Glucose Lactic Fermentation
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 fermentation also occurs in our muscles under high loads and lack of oxygen.
There are two types of this process. The first is homoenzymatic fermentation. If you ever heard the prefix "homo", then you probably understand what it means. Homoenzymatic fermentation is a process involving one enzyme. In the first stage, glycolysis occurs and pyruvic acid is formed. Then, the resulting pyruvate (in the solution this acid can exist only in the form of ions) is hydrogenated with NADH + H and lactate dehydrogenase. As a result, the recovery product is lactic acid, which is about 90% of all products obtained during the reaction. This compound, however, can also form in the form of two different 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.
We turn to the second type of lactic acid fermentation - heteroenzymatic. Several enzymes are involved in this process, and it 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 examined lactic acid fermentation. This is the process by which we can enjoy the taste of cottage cheese, yogurt, fermented baked milk and kefir. To summarize and write down in general terms the reaction of glucose lactic fermentation: C 6 H 12 O 6 = 2 C 3 H 6 O 3 . Of course, this is a simplified scheme of the process of homoenzymatic fermentation, since even the scheme of the heteroenzymatic process will be very complex. Chemists are still studying the milk fermentation of glucose and find out its full mechanisms, so we still have room for improvement.
Citric Fermentation
Reactions of this type of fermentation occur, as in alcohol, under the influence of fungi of a particular strain. The full mechanism of this reaction has not yet been fully studied, and we can only rely on some simplifications. However, there are suggestions that the initial stage of the process is glycolysis. Then pyruvic acid turns in turn into various acids and reaches citric acid. 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 follows: 2C 6 H 12 O 6 + 3O 2 = 2C 6 H 8 O 7 + 4H 2 O. Before this type of fermentation was discovered, people mined citric acid exclusively squeezing the fruits of the corresponding tree. However, in lemon this acid is not more than 15%, therefore this method was not practical, and after the discovery of this reaction, all acid was started to be obtained by fermentation.
Butyric acid fermentation
Let's move on to the next type. This type of fermentation occurs under the influence of butyric acid bacteria. They are widespread, and the process they trigger plays a key role in biologically important cycles. With the help of these bacteria, the decomposition of dead organisms occurs. Butyric acid, formed during 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 herself. However, butyric acid fermentation is not always beneficial. It can cause spoilage of vegetables, canned goods, milk and other products. But this can happen if only oil-acid bacteria enter the product.
Let's analyze the mechanism of glucose fermentation. His reaction is as follows: C 6 H 12 O 6 → CH 3 CH 2 CH 2 COOH + 2CO 2 ↑ + 2H 2 . As a result, energy is also formed, which ensures the vital activity of the butyric acid bacteria.
Acetone-butyl fermentation
This type is very similar to butyric acid. Not only glucose, but also glycerin and pyruvic acid can roam in this way. This process can be divided into two stages: the first (sometimes called acidic) is actually butyric acid 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 (acetone butyl). Since this whole process also occurs under the influence of bacteria, when acidifying the environment (increasing the concentration of acids), special enzymes are released by bacteria. They induce the reaction of converting the products of glucose fermentation to n-butanol (butyl alcohol) and acetone. In addition, some ethanol may form.
Other types of fermentation
In addition to these five types of this process, there are several more. For example, this is acetic fermentation. It also occurs under the influence of many bacteria. This type of fermentation can be used for beneficial purposes in pickling. It protects food from pathogenic and dangerous bacteria. Alkaline or methane fermentation is also distinguished. Unlike the previous types, this type of fermentation can be carried out for most organic compounds. As a result of a large number of complex reactions, organic matter is broken down into methane, hydrogen and carbon dioxide.
Biological role
Fermentation is the most ancient way of producing energy by living organisms. Some creatures produce organic substances, simultaneously receiving energy, while others destroy these substances, also receiving energy. Our whole life is built on this. And in each of us, fermentation in one form or another proceeds. As we said above, lactic fermentation occurs in the muscles during intense training.
What else to read?
If you are interested in the biochemistry of this very interesting process, it is worth starting with school textbooks in chemistry and biology. Many university textbooks contain such detailed material that after reading them you can simply become an expert in this field.
Conclusion
So we have come to an end. We examined 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.