Nature allows a person to enjoy the benefits that are available in it. At the same time, people are trying to increase these riches, create something new and learn about the unknown. Bacteria are the smallest creatures of nature, which people have also learned to use for their own purposes.
But not only the harm associated with pathogenic processes and diseases is carried 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 lactic acid fermentation of substances is carried out specifically.
History of occurrence and use of fermentation
The first mention that the fermentation process was used by people in order to obtain certain products appeared as early as 5000 BC. It was then that the Babylonians used this method to obtain products such as:
- cheese;
- wine;
- curdled milk and othersdairy products.
Later similar food was received in Egypt, China, Sudan, Mexico and other ancient states. They began to bake yeast bread, ferment vegetable crops, and the first attempts at canning appeared.
The process of lactic acid fermentation has been used by people for thousands of years. Cheeses, kefirs, yogurts have been an important part of the meal at all times. All 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 17th century, Van Helmont proposed to introduce the term "fermentation" for those cooking processes that are accompanied by the release of gas. After all, in translation, this word means "boiling." However, only in the 19th century, that is, almost two hundred years later, the French microbiologist, chemist and physicist Louis Pasteur discovered the existence of microbes, bacteria to the world.
It has since become known that different types of fermentation require 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 right direction for a person.
The essence of fermentation processes
If we talk about what the fermentation process is, then we should point out its biochemical nature. After all, at its core, this is just the activity of bacteria that extract energy for themselves for life, while producing variousby-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 be the result, is determined by the type of process itself. There are several fermentation options, so there is a classification for these transformations.
Classification
There are three main types of fermentation.
- Alcohol. It consists in the oxidation of the original carbohydrate molecule to ethyl alcohol, carbon dioxide, water and an ATP molecule (an energy source). These transformations are carried out under the action of not only bacteria, but also fungi of various genera and species. It is in this way that products such as beer, wine, baking yeast, and alcohol have been obtained since ancient times. The energy that is released during the decomposition of carbohydrates goes to ensure the vital processes of the microorganism. This is the biological essence of the process.
- Lactic acid fermentation is the oxidation of carbohydrates to lactic acid with the release of a number of by-products. How it is carried out and what types it 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 bacteria that live in anaerobic conditions at the bottom of swamps, river silt, and so on. Thanks to their work in nature, a huge amount of organic components is processed. Products are many substances, the main among whichbutyric acid. Also emitted: acetone, isopropyl alcohol, carbon dioxide, acetic acid, lactic acid, ethyl alcohol and other compounds.
Each of the designated types is important both natural and industrial scale. The types of organisms that carry out such transformations are well studied today, and many of them are cultivated artificially in order to obtain a high yield of the product.
Lactic acid fermentation: a general concept
This type of fermentation has been known since antiquity. Even before our era, the inhabitants of Ancient Egypt and other states knew how to make cheese, brew beer and wine, bake bread, ferment vegetables and fruits.
Today, special starter cultures are used for fermented milk products, strains of the necessary microorganisms are artificially grown. The process has been modernized and brought to automatism, carried out with the help of complete equipment. There are many manufacturers that directly produce lactic acid fermentation.
The essence of the whole process can be summarized in several paragraphs.
- A carbohydrate is taken as the main product - simple (fructose, glucose, pentoses) or complex (sucrose, starch, glycogen and others).
- Anaerobic conditions are created.
- Strains of lactic acid bacteria 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 additionalcomponents, pressure.
- After the fermentation process is completed, the product is processed and all side compounds are isolated.
Of course, this is just a general description of what is happening. In fact, many complex biochemical reactions take place at each stage, because the process of lactic acid fermentation is the result of the vital activity of living beings.
Basics of the lactic acid fermentation process
From a chemical point of view, these transformations are a series of successive stages.
- First, there is a change in the original substrate, 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 rearranged into gluconic acid.
- Oxidation-reduction reactions, accompanied by the release of gases, the formation of by-products. The main unit in the whole process is lactic acid. It is she who is produced and accumulates during fermentation. However, this is not the only connection. So, there is the formation of molecules of acetic acid, ethyl alcohol, carbon dioxide, water, and sometimes other accompanying ones.
- Energy output of the process in the form of molecules of adenosine triphosphoric acid (ATP). There are 2 ATP molecules per molecule of glucose, but if the initial substrate is of a more complex structure, for example cellulose, then there are three ATP molecules. This energy is used by lactic acid bacteria for further life.
It is natural thatif one understands biochemical transformations in detail, then all intermediate molecules and complexes should be indicated. Such as:
- pyruvic acid;
- adenosine diphosphate;
- molecules of nicotinamine diphosphate as a carrier of hydrogen and others.
However, this issue deserves special attention and should be considered from the point of view of biochemistry, so we will not touch it in this article. Let's take a closer look at what is the technology for the production of lactic acid products and what types of fermentation in question exist.
Homofermentative fermentation
Homofermentative lactic acid fermentation involves the use of special forms of pathogens and differs from heterofermentative in the resulting products and their quantity. It occurs along the glycolytic pathway inside the cell of the microorganism. The bottom line is, as in general with any fermentation, the conversion of carbohydrates into 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.
Bacteria fermentation of this type of the following species:
- Streptococcus lactis.
- Lactobacillus casei.
- Lactobacillus acidophilus and others.
What other substances are formed as a result of homofermentative fermentation? These are connections like:
- ethyl alcohol;
- volatile acids;
- carbon dioxide;
- fumaric and succinic acid.
However, this method of obtaining fermented milk products is practically not used in industry. It is preserved in nature as the initial stage of glycolysis, it also occurs in mammalian muscle cells during extensive physical exertion.
The technology for the production of the necessary products for human nutrition involves the use of such initial carbohydrates as:
- glucose;
- sucrose;
- fructose;
- mannose;
- starch and some others.
And homofermentative 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, thanks to which the production of all fermented milk products is carried out, vegetables are preserved, and silage feed for livestock is harvested.
The main difference from that described earlier is that pathogens carry out lactic acid fermentation with the formation of a larger number of by-products. Only 50% of sugar is processed by bacteria into lactic acid, the rest goes to the formation of molecules such as:
- acetic acid;
- glycerin;
- carbon dioxide;
- ethyl alcohol and others.
How is it better and more profitable than the formation of 90% pure lactic acid with the homofermentative method? The thing is that when the main product is producedtoo much, then the vital activity of many bacteria is completely inhibited. In addition, products lose many of the taste qualities that they acquire due to side compounds. So, for example, the pleasant aroma of canned vegetables is provided by acetic acid and isoamyl alcohol. If these compounds are not present, then the result of conservation will be completely different.
A yield of lactic acid of 50% is quite sufficient to suppress the development and vital 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 can exist, except for lactic acid bacteria. The whole process is carried out along the pentose phosphate pathway.
The fermentation conditions for the heterofermentative method should be as follows:
- good and fresh starter added at the initial stage;
- optimal external conditions that are selected for each product individually;
- high-quality and well-functioning equipment;
- all technical devices necessary for the process.
Among external conditions, process temperature is of particular importance. It should not be too high, but the cold will drastically slow down the entire course of fermentation.
Today there is a specialized fermentation tank that automatically creates all the necessary conditions for the proper and comfortable functioning of microorganisms.
Equipment required
As we noted above, among the most important attributesshould be noted capacity for fermentation. If we talk about the home procedure, then you should pay attention to the cleanliness of the dishes used during preservation, the manufacture of yogurt and other products. One way to reduce the number of extraneous populations of microorganisms is to sterilize containers before using them.
Which dishes are suitable for heterofermentative fermentation? It can be a glass or high-quality plastic (polypropylene, polyethylene) container that can be tightly closed with a lid.
Industry uses special devices to disinfect and clean containers before starting the fermentation process.
Bacteria used in the process
If we talk about bacterial cultures that are used to create canned and fermented milk products, then we can identify several of the most common types of organisms.
- Acidophilic bulgarian stick.
- Lactobacillus species Sporolactobacillus inulinus.
- Bifidobacteria.
- Leukostocks.
- Lactic acid cocci.
- Lactobacillus species L. Casei.
- Bacteria of the genus Streptococcus and others.
Based on the combination and pure cultures of the indicated organisms, starter cultures for fermented milk products are made. They are in the public domain, anyone can buy them. The most important thing is to observe the conditions of the fermentation process in order to benefit from the resultingproduct.
What products are obtained from this fermentation?
If we talk about what fermentation products can be obtained with the help of lactobacilli, then we can name several main categories.
- Fermented milk products (fermented baked milk, yoghurts, varenets, kefir, cottage cheese, sour cream, butter, acidophilus products and others).
- Silo-type feed for farm animals.
- Lactic acid, which is used in the manufacture of soft drinks, dressing fur skins and more.
- Baking, cheese production.
- Canned fruits and vegetables.
All this proves the importance of certain types of bacteria in people's lives, their industrial activities.
