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MOST IMPORTANT SCIENTIFIC DISCOVERIES
Biological theory of fermentation. History and essence of scientific discovery
Directory / The most important scientific discoveries In 1680 a Dutchman Anthony Van Leeuwenhoek I first saw brewer's yeast in my homemade microscope. He described them in a letter to the Royal Society and gave a drawing showing budding round cells forming clusters. Thus began the study of yeast morphology. These observations were far ahead of the state of science at the time. It was only in 1835 that the reports of Cañard de Latour in France, Schwann and Kützing in Germany appeared, in which it was proved that yeasts belong to lower plant organisms that have a nucleus, multiply by budding on nutrient media containing sugar, and cause fermentation. However, this biological direction in research related to the elucidation of the causes of fermentation did not receive universal recognition in the first half of the XNUMXth century. In the middle of the nineteenth century, the chemical theory of fermentation was widespread. For example, Stahl argued that decaying substances can transmit this state to another substance that is not currently decaying. Decay is accompanied by movement, and the ability to cause putrefaction is associated with the transfer of movement to a body at rest. Enzymes are also in motion, and their ability to cause fermentation is related to the transmission of motion. The prominent chemists of the time Liebig and Berzelius developed this point of view. Berzelius did not see a fundamental difference between different types of fermentation and putrefaction - all these are different stages of the same process. Fermentation is possible only under two conditions: the medium must contain gluten or other nitrogenous organic matter and the fermented liquid containing gluten must be exposed to atmospheric oxygen. In this case, an insoluble precipitate is formed at the bottom of the vessel, capable of causing a new fermentation. Liebig associated all fermentation processes with the decomposition and decay of organic substances, the latter, undergoing decay, become enzymes and can already cause fermentation of non-rotting substances, such as sugar. When the decaying substances come into contact with the fermentable, the latter disintegrates into particles. Liebig did not deny that yeast is needed for the fermentation of sugar, but not necessarily living ones, since it is dying and decaying yeast that causes fermentation, like any rotting substance. Such, in the most general terms, are the foundations of the chemical theory of fermentation until the French scientist Pasteur began his research on fermentation. Louis Pasteur (1822-1895) was born in the French town of Dole. Louis grew up in a large friendly family. Despite poor health and lack of funds, Pasteur successfully completed his studies, first at a college in Arbois, and then in Besançon. After graduating here with a bachelor's degree, in 1843 he entered the Higher Normal School, which trains teachers for high schools. After graduating from school in 1847, Pasteur passed the exams for the title of assistant professor of physical sciences. And a year later he defended his doctoral dissertation. Then Pasteur was not yet 26 years old, but he had already gained fame for his research in the field of crystal structure. The young scientist gave an answer to a question that had remained unresolved before him, despite the efforts of many leading scientists. He discovered the reason for the unequal influence of a beam of polarized light on the crystals of organic substances. This outstanding discovery later led to the emergence of stereochemistry - the science of the spatial arrangement of atoms in molecules. Also in 1848, Pasteur became associate professor of physics at Dijon. Three months later, he takes up a new position as associate professor of chemistry in Strasbourg. Pasteur took an active part in the revolution of 1848 and even joined the National Guard. In 1854, Pasteur was appointed dean of the newly organized Faculty of Physics and Mathematics at the University of Lille. This region of France was famous for its sugar and fermentation industries. The owners of local factories repeatedly turned to Pasteur with a request to help rationalize production, improve it, guided by the latest achievements of science. Getting acquainted with the work of factories, Pasteur could not help but come to the conclusion that modern scientific knowledge in this area was more than modest, and this prompted him to start studying fermentations. He began to study this issue. The result of his research was a monograph. The first published memoir was devoted to lactic acid fermentation. It made a particularly big impression in the scientific world, since it was a new fermentation - all previous research dealt with predominantly alcoholic fermentation. “Pasteur conducted all his research on fermentations in order to find out to what extent his own experimental data can confirm or refute the chemical theory of fermentations,” writes A.A. Imshenetsky in his work on the scientist. “The results of his experiments can be summarized as follows. 1. For the occurrence of fermentation, air, contrary to the opinion of supporters of the chemical theory of fermentation, is not needed. Lactic acid fermentation proceeds without access to air in the same way as alcohol. This allows us to give the general formula "fermentation is life without oxygen." To substantiate this thesis, the discovery by Pasteur of butyric fermentation, caused by strictly anaerobic bacteria, which not only do not need oxygen, but the latter acts on them like a poison, was of exceptional importance. Prior to this discovery, it was believed that life without oxygen was impossible, and it was no coincidence that Gay-Lussac associated the resistance of products in Apper canned food to decay with the absence of oxygen in cans. The discovery of anaerobiosis met with strong objections from Brefeld and other scientists, but it turned out to be so convincing that it was soon recognized by everyone. 2. Each fermentation is caused by a specific pathogen. Pasteur first established that lactic acid fermentation is associated with the development of microbes that differ in their morphology from yeast. Butyric acid is formed as a result of the vital activity of a special type of microbe. Acetic acid and alcoholic fermentations, as well as urea fermentation, have their pathogens. There is nothing surprising in the fact that Pasteur, based on the current state of the taxonomy of lower plant organisms, did not always give the correct names to the organisms he described. So, he attributed butyric acid bacteria to representatives of the animal world, designated acetic acid bacteria as Mycoderma, etc. All this did not change the main conclusion - various fermentations are caused by various microbes. 3. Fermentation is associated with the life of microbes, with their reproduction, and not with death and decomposition, as the supporters of the chemical theory of fermentation believed. The weight of microbes during fermentation is constantly increasing and the substances fermented by them are also used by the yeast to build their body. 4. For fermentation, the presence of particles of protein substances (gluten) in the medium is not necessary at all, which, according to adherents of the chemical theory, set in motion and, transferring it to other particles, thereby cause fermentation or decay. Fermentation of sugar with the formation of alcohol or lactic acid can occur in a medium that does not contain protein at all, but has an inorganic compound as the only source of nitrogen, for example, ammonium sulphate. The results of Pasteur's experimental studies dealt a decisive blow to Liebig's theory. Its adherents could no longer explain fermentation by the transmission of the movement of particles and associate it with death, with the decomposition of putrefying substances. But already at the very beginning of the sixties, Berthelot expressed the idea directly that such a limited biological point of view should not satisfy the physiologist, and even more so the chemist. Based on thermochemical data, Berthelot argued that the fermentation and vital activity of yeast cells are not related to each other, since for the synthesis of the living substance of yeast there is no need for an influx of energy from outside. The development of biochemistry and fermentology more and more prompted prominent scientists to return to Berthelot's ideas. Gradually, the number of discovered "soluble enzymes", i.e., enzymes, increased, and it became possible to carry out cell-free hydrolysis of di- and polysaccharides, protein decomposition, and various oxidative processes. All this led to the fact that K.A. Timiryazev in a lecture in 1895 stated: "... Berthelot, arguing with Pasteur, pointed out that the view of fermentation as a chemical process underlying the physiological phenomenon that Pasteur observed - that this view follows from the inevitable historical course of development of all sciences and, in particular, physiology, according to which complex phenomena are reduced to simple ones and, consequently, physiological - to physical and chemical ones. And, as we see, history already justifies the correctness of this reference to it by Berthelot ... " It must be said that Pasteur never denied the participation of enzymes in fermentation. Yes, it would be illogical, since, being a chemist, he could not imagine the transformation of a molecule into alcohol without a chain of chemical reactions that take place inside the cell: "... I will add that it has always been a mystery to me on what basis they think that I would be embarrassed if the discovery of soluble enzymes in fermentation were made, or if the conversion of sugar into alcohol were proved independently of the vital activity of the cell. There is no doubt that the study of cell-free fermentation, studies with yeast juice and other preparations have yielded a lot of value. It was they who made it possible to establish that fermentation scheme, in particular alcohol, which was included in all manuals and is now generally recognized. “But all these studies answer the question “how” this process occurs,” notes A.A. Imshenetsky, “but do not answer the question “why” this harmonious, this extremely complex functioning of enzymes inside the yeast cell became possible and “why "Those or other fermentation processes arose. This is just a detailing of the main idea that Pasteur developed then, and not a contrast between the chemical theory of fermentation and the biological one. Pasteur for the first time, as a brilliant biologist, gave an exhaustive answer why fermentations arose. He explained the expediency of these processes and showed that they are necessary for the life of cells, and if they were not of an adaptive nature, they could not arise in nature. This is sometimes forgotten in chemical research. Pasteur pointed out the energetic significance of fermentations and showed that they have an ecological significance. In his studies, he repeatedly notes the great role played by the products of their own vital activity of fermenting microorganisms in changing the environment. Establishing that one type of microbe displaces another by the products of its own vital activity, Pasteur solves one of the most interesting ecological problems. It should also be noted here that, unlike contemporary German researchers, he abandoned the search for a universal nutrient medium on which all types of microbes could grow without exception, and for the first time applied the medium based on ecology, i.e., the conditions for the existence of microbes . Therefore, we have the right to consider Pasteur also the founder of the still developing young branch of microbiology - the ecology of microorganisms. Unraveling the phenomena of fermentation was of great practical importance not only for French winemaking, which suffered huge losses from "wine diseases", but also played an exceptional role in the development of biological science, the practice of agriculture and industry. Deep knowledge of the nature of fermentations makes it possible to control their processes. This is very important for baking, winemaking, and the manufacture of many food substances. Author: Samin D.K.
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