Nature allows man to use the benefits that are in it. At the same time, people are trying to increase these wealth, create something new and learn something else unknown. Bacteria are the smallest creatures of nature, which man also learned to use for his own purposes.
But not only the harm associated with pathogenic processes and diseases are caused by these prokaryotic organisms. They are also the source of an important industrial process that has been used by people since ancient times - fermentation. In this article we will consider what this process is and how specifically the lactic fermentation of substances is carried out.
History of the origin and use of fermentation
The first mention of the fact that the fermentation process was used by people in order to obtain certain products appeared as far back as 5000 BC. It was then that the Babylonians used this method to obtain products such as:
- cheese;
- wine;
- yogurt and other dairy products.
Later, similar food began to be received in Egypt, China, Sudan, Mexico and other ancient states. They began to bake yeast bread, ferment vegetables, the first attempts at canning appeared.
The process of lactic acid fermentation has been used by people for thousands of years. Cheeses, kefir, yogurt have been an important part of the meal at all times. All the doctors and healers knew about the benefits of these products. However, the reasons why this kind of transformation is possible remained unknown for a long time.
The fact that fermentation conditions require the presence of microorganisms, people could not even imagine. In the middle of the XVII century, Van Helmont will propose to introduce the term "fermentation" for those cooking processes that are accompanied by gas evolution. Indeed, in translation this word means "boiling". However, only in the XIX century, that is, almost two hundred years later, the French microbiologist, chemist and physicist Louis Pasteur discovered the world of microbes, bacteria.
Since then it has become known that different fermentation requires the presence of various kinds of microorganisms invisible to the eye. Their study made it possible over time to control fermentation and direct it in the direction necessary for man.
The essence of fermentation processes
If we talk about what constitutes the fermentation process, then we should indicate its biochemical nature. After all, in essence, it is simply the activity of bacteria that produce energy for themselves, while producing various by-products.
In general, fermentation can be described in one word - oxidation. Anaerobic decomposition of a substance under the influence of certain bacteria, which leads to the formation of a number of products. What substance is the basis, as well as what will result, is determined by the type of process itself. There are several options for fermentation, so there is a classification for these transformations.
Classification
There are three main types of fermentation.
- Alcohol It consists in the oxidation of the initial carbohydrate molecule to ethanol, carbon dioxide, water and the ATP molecule (energy source). These transformations are carried out under the influence of not only bacteria, but also fungi of various genera and species. In this way, from ancient times, such products as beer, wine, yeast for baking, and alcohol have been obtained. The energy that is released during the decomposition of carbohydrate goes to providing the vital processes of the microorganism. This is precisely the biological essence of the process.
- Lactic acid fermentation consists in the oxidation of carbohydrates to lactic acid with the release of a number of by-products. How it is carried out and what types happens, we will consider in more detail further.
- Butyric acid . This type of fermentation is important on a natural scale. It is carried out due to the vital activity of butyric acid bacteria that live in anaerobic conditions at the bottom of swamps, river silt, and so on. Thanks to their work, a huge amount of organic components are processed in nature. Products are many substances, mainly butyric acid. Also distinguished: acetone, isopropyl alcohol, carbon dioxide, acetic acid, lactic, ethyl alcohol and other compounds.
Each of the indicated types is important both natural and industrial scale. The species of organisms carrying out such transformations have been well studied to date and many of them are cultivated artificially in order to obtain a large yield of the product.
Lactic Fermentation: A General Concept
This type of fermentation has been known since antiquity. Even before our era, the inhabitants of Ancient Egypt and other countries knew how to make cheese, brew beer and wine, bake bread, and ripen vegetables and fruits.
Today, special starter cultures for fermented milk products are used, strains of the necessary microorganisms are artificially grown. The process is modernized and brought to automatism, it is carried out with the help of a complete set of equipment. There are many manufacturers that directly produce lactic acid fermentation.
The essence of the whole process can be stated in several points.
- For the main product, the initial carbohydrate is taken - simple (fructose, glucose, pentose) or complex (sucrose, starch, glycogen and others).
- Anaerobic conditions are created.
- Lactic acid bacteria strains of a certain type are added to the product.
- All necessary external factors are provided that are optimal for the desired product: illumination, temperature, the presence of certain additional components, pressure.
- After the fermentation process is completed, the product is processed and all side compounds are isolated.
Of course, this is only a general description of what is happening. In fact, at each stage there are many complex biochemical reactions, because the process of lactic acid fermentation is the result of the vital activity of living beings.
The Basics of Lactic Fermentation
From a chemical point of view, these transformations are a series of successive stages.
- First, a change in the initial substrate occurs, that is, the carbon chain of the substance (carbohydrate) changes. This leads to the appearance of intermediate compounds of a completely different nature, belonging to different classes. For example, if the initial substrate is glucose, then it is converted to gluconic acid.
- Redox reactions accompanied by gas evolution, formation of by-products. The basic unit throughout the process is lactic acid. It is it that is produced and accumulates during fermentation. However, this is not the only connection. So, the formation of molecules of acetic acid, ethyl alcohol, carbon dioxide, water, and sometimes other accompanying molecules.
- The energy output of the process in the form of adenosine triphosphoric acid (ATP) molecules. There are 2 ATP molecules per glucose molecule, but if the initial substrate is of a more complex structure, for example cellulose, then three ATP molecules. This energy is used by lactic acid bacteria for further life.
Naturally, if one understands biochemical transformations in detail, then all intermediate molecules and complexes should be indicated. Such, for example, as:
- pyruvic acid;
- adenosine diphosphate;
- Nicotinamine diphosphate molecules as a hydrogen carrier and others.
However, this issue deserves special attention and should be considered from the point of view of biochemistry; therefore, we will not touch upon it in this article. Let us consider in more detail what is the technology for the production of lactic acid products and what types of fermentation under consideration exist.
Homoenzymatic fermentation
Homoenzymatic fermentation of lactic acid involves the use of special forms of pathogens and differs from heteroenzymatic fermentation products and their quantity. It occurs along the glycolytic pathway inside the cell of the microorganism. The essence is, as with any fermentation as a whole, in the conversion of carbohydrates to lactic acid. The main advantage of this process is that the yield of the desired product is 90%. And only the rest goes to side compounds.
Fermentation bacteria of this type of the following types:
- Streptococcus lactis.
- Lactobacillus casei.
- Lactobacillus acidophilus and others.
What other substances are formed as a result of homoenzymatic fermentation? These are compounds such as:
- ethanol;
- volatile acids;
- carbon dioxide;
- fumaric and succinic acid.
However, in industry, this method of producing dairy products is practically not used. It was preserved in nature as the initial stage of glycolysis, it also occurs in mammalian muscle cells with extensive physical exertion.
The production technology of the right products for human nutrition involves the use of such starting carbohydrates as:
- glucose;
- sucrose;
- fructose;
- mannose;
- starch and some others.
And homoenzymatic bacteria are not able to oxidize many of these compounds, so their use as starter cultures in production is not possible.
Heterofermentative lactic acid fermentation
This method is precisely the industrially applicable one, due to which the production of all fermented milk products is carried out, vegetables are preserved, silage feed for livestock is harvested.
The main difference from the previously described is that lactic acid fermentation is carried out by pathogens with the formation of a larger number of by-products. Only 50% of the sugar is processed by bacteria into lactic acid, the rest goes to the formation of such molecules as:
- acetic acid;
- glycerol;
- carbon dioxide;
- ethyl alcohol and others.
What is better and more profitable than the formation of 90% pure lactic acid with the homoenzymatic method? The thing is that when too much of the main product is produced, the vital activity of many bacteria is completely inhibited. In addition, the products lose many of the taste qualities that are acquired due to side compounds. So, for example, the pleasant aroma of canned vegetables is provided by acetic acid and isoamyl alcohol. If these compounds do not exist, then the result of conservation will be completely different.
A 50% yield of lactic acid is quite sufficient to suppress the development and activity of all extraneous fungi and microorganisms in the system. Because even 1-2% cause too strong acidification of the environment in which no other organisms except lactic acid bacteria can exist. The whole process is carried out along the pentose phosphate pathway.
The fermentation conditions with the heterozymatic method should be as follows:
- good and fresh sourdough, added at the initial stage;
- optimal external conditions that are selected for each product individually;
- high-quality and debugged equipment;
- all necessary technical devices for the process.
Among external conditions, the process temperature is of particular importance. It should not be too high, but the cold will sharply inhibit the entire course of fermentation.
Today, there is a specialized capacity for fermentation, which automatically creates all the necessary conditions for the correct and comfortable operation of microorganisms.
Necessary equipment
As we have noted above, among the most important attributes, a fermentation tank should be noted. If we talk about the home procedure, then you should pay attention to the cleanliness of the dishes used in the preservation, manufacture of yogurt and other products. One way to reduce the number of extraneous populations of microorganisms is to sterilize the containers before using them.
What kind of cookware is suitable for heterozymatic fermentation? This can be a glass or high-quality plastic (polypropylene, polyethylene) container, which is capable of tightly closing with a lid.
In industry, special devices are used to disinfect and empty containers before starting the fermentation process.
Bacteria used in the process
If we talk about the cultures of bacteria that are used to create canned and fermented milk products, then we can identify some of the most common types of organisms.
- Acidophilic Bulgarian stick.
- Lactobacillus species Sporolactobacillus inulinus.
- Bifidobacteria.
- Leucostats.
- Lactic Cocci.
- Lactobacillus species L. Casei.
- Bacteria of the genus Streptococcus and others.
Based on the combination and pure cultures of the designated organisms, sourdough is made for fermented milk products. They are in the public domain, they can be purchased by anyone. The most important thing is to observe the conditions of the fermentation process in order to benefit from the resulting product.
What products get as a result of such fermentation?
If we talk about what fermentation products can be obtained with the help of lactobacilli, then there are several main categories.
- Sour-milk food products (fermented baked milk, yoghurts, Varents, kefir, cottage cheese, sour cream, butter, acidophilic products and others).
- Silage feed for farm animals.
- Lactic acid, which is used in the manufacture of soft drinks, dressing fur skins and more.
- Bakery, cheese production.
- Preservation of fruits and vegetables.
All this proves the importance of bacteria of certain species in the life of people, their industrial activities.