A helpful bioinformatics tool MEGA 6 was also used to generate phylogenetic trees able to determine the evolutionary relationship of yeasts obtained from their experiments.
Biofuel production by recombinant Saccharomyces cerevisiae strains with essential genes and metabolic networks for xylose metabolism has been also reported [ 23 ]. Moreover, the door is opened to provide new targets for engineering other xylose-fermenting strains. The utilization of xylose, the second most abundant sugar component in the hydrolysates of lignocellulosic materials, is a relevant issue. Understanding the relationship between xylose and the metabolic regulatory systems in yeasts is a crucial aspects where hexokinase 2 Hxk2p is involved [ 25 ].
All of these processes can be damaged if contaminated. Because most fermentation substrates are not sterile, contamination is always a factor to consider.
With a very interesting approach, a genetically modified strain of Komagataella phaffii yeast was used for the use of glycerol as a base substance in lactate production. Polyactide, a bioplastic widely used in the pharmaceutical, automotive, packaging and food industries was produced. The disruption of the gene encoding arabitol dehydrogenase ArDH was achieved, which improves the production of lactic acid by K. Seo et al. This review includes information on industrial uses of yeast fermentation, microbial contamination and its effects on yeast fermentations.
Finally, they describe strategies for controlling microbial contamination. Thanks to all the authors and reviewers for their excellent contributions to this Special Issue. Additional thanks to the Microorganisms Editorial Office for their professional assistance and continuous support. National Center for Biotechnology Information , U. Journal List Microorganisms v. Published online Jul Sergi Maicas. Author information Article notes Copyright and License information Disclaimer. Received Jul 17; Accepted Jul This article has been cited by other articles in PMC.
Abstract In recent years, vessels have been discovered that contain the remains of wine with an age close to years. Keywords: yeast, non- Saccharomyces yeast, wine, beer, beverages. Introduction Fermentation is a well-known natural process used by humanity for thousands of years with the fundamental purpose of making alcoholic beverages, as well as bread and by-products. Open in a separate window.
Figure 1. Yeasts Yeasts are eukaryotic microorganisms that live in a wide variety of ecological niches, mainly in water, soil, air and on plant and fruit surfaces. Non- Saccharomyces Yeasts Non- Saccharomyces yeasts are a group of microorganisms used in numerous fermentation processes, since their high metabolic differences allow the synthesis of different final products.
Yeast Fermentation Processes 2. Alcoholic Fermentations The production of alcoholic beverages from fermentable carbon sources by yeast is the oldest and most economically important of all biotechnologies. Beer Fermentation Beer is the most consumed alcoholic beverage worldwide.
Cider Fermentation Cider is another alcoholic beverage derived from the apple fruit industry, very popular in different countries in the world, mainly Europe, North America, and Australia [ 11 ]. Non-Alcoholic Fermentations Moreover, yeast can act in the fermentation of global non-alcoholic products bread, chocolate or coffee, beverages such as kefir, sodas, lemonades, and vinegar or even biofuels and other chemicals.
Bread Fermentation The fermentation of the dough made by the yeasts is the most critical phase in the making of bread. Coffee Fermentation Yeasts play an important role in coffee production, in the post-harvest phase. Chocolate Fermentation Raw cacao beans have a bitter and astringent taste, because of high phenolic content. Not Only Food: Biofuels and Other Chemicals The fermentation processes of substrates such as xylose are also of high interest on an industrial level.
Acknowledgments Thanks to all the authors and reviewers for their excellent contributions to this Special Issue.
Conflicts of Interest The editors declares no conflict of interest. References 1. Puligundla P. Very high gravity VHG ethanolic brewing and fermentation: A research update. Walker G. Saccharomyces cerevisiae in the Production of Fermented Beverages.
Ciani M. Oenological properties of non-Saccharomyces yeasts associated with wine-making. World J. Grangeteau C. FT-IR spectroscopy: A powerful tool for studying the inter- and intraspecific biodiversity of cultivable non-Saccharomyces yeasts isolated from grape must. Estela-Escalante W. Evaluation of the potential production of ethanol by Candida zemplinina yeast with regard to beer fermentation.
Cordero-Bueso G. Biotechnological potential of non-Saccharomyces yeasts isolated during spontaneous fermentations of Malvar Vitis vinifera cv. Food Res. Yeast interactions in inoculated wine fermentation. Canonico L. Torulaspora delbrueckii in the brewing process: A new approach to enhance bioflavour and to reduce ethanol content. Food Microbiol. Dzialo M. Physiology, ecology and industrial applications of aroma formation in yeast.
FEMS Microbiol. Libkind D. Microbe domestication and the identification of the wild genetic stock of lager-brewing yeast. Cousin F. Microorganisms in fermented apple beverages: Current knowledge and future directions. Lorenzini M. Assessment of yeasts for apple juice fermentation and production of cider volatile compounds.
Genetic and phenotypic diversity of autochthonous cider yeasts in a cellar from Asturias. Gensi R. Traditional production method and storage characteristics for banana beer tonto in Uganda.
Acta Hortic. Struyf N. Food Sci. Homeostasis Higher Level 7: Nucleic Acids 1. DNA Structure 2. Transcription 3. Translation 8: Metabolism 1. Metabolism 2. Cell Respiration 3. Photosynthesis 9: Plant Biology 1. Xylem Transport 2.
Phloem Transport 3. Plant Growth 4. Plant Reproduction Genetics 1. Meiosis 2. Inheritance 3. Speciation Animal Physiology 1. Antibody Production 2. Movement 3.
The chemists hypothesized that the yeast initiated alcoholic fermentation but did not take part in the reaction.
They assumed that the yeast remained unchanged throughout the chemical reactions. Gay-Lussac was experimenting with a method developed by Nicolas Appert, a confectioner and cooker, for preventing perishable food from rotting.
Gay-Lussac was interested in using the method to maintain grape juice wort in an unfermented state for an indefinite time. The method consisted of boiling the wort in a vessel, and then tightly closing the vessel containing the boiling fluid to avoid exposure to air.
With this method, the grape juice remained unfermented for long periods as long as the vessel was kept closed. However, if yeast ferment was introduced into the wort after the liquid cooled, the wort would begin to ferment. There was now no doubt that yeast were indispensable for alcoholic fermentation.
But what role did they play in the process? When more powerful microscopes were developed, the nature of yeast came to be better understood. In , Charles Cagniard de la Tour, a French inventor, observed that during alcoholic fermentation yeast multiply by gemmation budding.
His observation confirmed that yeast are one-celled organisms and suggested that they were closely related to the fermentation process. The recognition that yeast are living entities and not merely organic residues changed the prevailing idea that fermentation was only a chemical process.
This discovery paved the way to understand the role of yeast in fermentation. Figure 2: Louis Pasteur Our modern understanding of the fermentation process comes from the work of the French chemist Louis Pasteur. Life out of nowhere? Nature , Our modern understanding of the fermentation process comes from the work of the French chemist Louis Pasteur Figure 2.
Pasteur was the first to demonstrate experimentally that fermented beverages result from the action of living yeast transforming glucose into ethanol. Moreover, Pasteur demonstrated that only microorganisms are capable of converting sugars into alcohol from grape juice, and that the process occurs in the absence of oxygen. He concluded that fermentation is a vital process, and he defined it as respiration without air Barnett ; Pasteur Pasteur performed careful experiments and demonstrated that the end products of alcoholic fermentation are more numerous and complex than those initially reported by Lavoisier.
Along with alcohol and carbon dioxide, there were also significant amounts of glycerin, succinic acid, and amylic alcohol some of these molecules were optical isomers — a characteristic of many important molecules required for life. These observations suggested that fermentation was an organic process. To confirm his hypothesis, Pasteur reproduced fermentation under experimental conditions, and his results showed that fermentation and yeast multiplication occur in parallel.
He realized that fermentation is a consequence of the yeast multiplication, and the yeast have to be alive for alcohol to be produced. In , a man named Bigo sought Pasteur's help because he was having problems at his distillery, which produced alcohol from sugar beetroot fermentation. The contents of his fermentation containers were embittered, and instead of alcohol he was obtaining a substance similar to sour milk. Pasteur analyzed the chemical contents of the sour substance and found that it contained a substantial amount of lactic acid instead of alcohol.
When he compared the sediments from different containers under the microscope, he noticed that large amounts of yeast were visible in samples from the containers in which alcoholic fermentation had occurred.
In contrast, in the polluted containers, the ones containing lactic acid, he observed "much smaller cells than the yeast. Alcoholic fermentation occurs by the action of yeast; lactic acid fermentation, by the action of bacteria. By the end of the nineteenth century, Eduard Buchner had shown that fermentation could occur in yeast extracts free of cells, making it possible to study fermentation biochemistry in vitro.
He prepared cell-free extracts by carefully grinding yeast cells with a pestle and mortar. The resulting moist mixture was put through a press to obtain a "juice" to which sugar was added.
Using a microscope, Buchner confirmed that there were no living yeast cells in the extract. Upon studying the cell-free extracts, Buchner detected zymase, the active constituent of the extracts that carries out fermentation.
He realized that the chemical reactions responsible for fermentation were occurring inside the yeast. Today researchers know that zymase is a collection of enzymes proteins that promote chemical reactions. Enzymes are part of the cellular machinery, and all of the chemical reactions that occur inside cells are catalyzed and modulated by enzymes. ATP is a versatile molecule used by enzymes and other proteins in many cellular processes.
Glycolysis — the metabolic pathway that converts glucose a type of sugar into pyruvate — is the first major step of fermentation or respiration in cells. It is an ancient metabolic pathway that probably developed about 3. Because of its importance, glycolysis was the first metabolic pathway resolved by biochemists.
The scientists studying glycolysis faced an enormous challenge as they figured out how many chemical reactions were involved, and the order in which these reactions took place. In glycolysis, a single molecule of glucose with six carbon atoms is transformed into two molecules of pyruvic acid each with three carbon atoms. In order to understand glycolysis, scientists began by analyzing and purifying the labile component of cell-free extracts, which Buchner called zymase.
They also detected a low-molecular-weight, heat-stable molecule, later called cozymase. Both components were required for fermentation to occur. The complete glycolytic pathway, which involves a sequence of ten chemical reactions, was elucidated around In glycolysis, two molecules of ATP are produced for each broken molecule of glucose. During glycolysis, two reduction-oxidation redox reactions occur.
In a redox reaction, one molecule is oxidized by losing electrons, while the other molecule is reduced by gaining those electrons. A molecule called NADH acts as the electron carrier in glycolysis, and this molecule must be reconstituted to ensure continuity of the glycolysis pathway.
Figure 3: Alternative metabolic routes following glycolysis A budding yeast cell is shown with the aerobic and anaerobic metabolic pathways following glycolysis. The nucleus black and mitochondrion red are also shown. When oxygen is available, pyruvic acid enters a series of chemical reactions known as the tricarboxylic acid cycle and proceeds to the respiratory chain. As a result of respiration, cells produce 36—38 molecules of ATP for each molecule of glucose oxidized.
In the absence of oxygen anoxygenic conditions , pyruvic acid can follow two different routes, depending on the type of cell. It can be converted into ethanol alcohol and carbon dioxide through the alcoholic fermentation pathway, or it can be converted into lactate through the lactic acid fermentation pathway Figure 3.
Since Pasteur's work, several types of microorganisms including yeast and some bacteria have been used to break down pyruvic acid to produce ethanol in beer brewing and wine making. The other by-product of fermentation, carbon dioxide, is used in bread making and the production of carbonated beverages.
Humankind has benefited from fermentation products, but from the yeast's point of view, alcohol and carbon dioxide are just waste products. As yeast continues to grow and metabolize sugar, the accumulation of alcohol becomes toxic and eventually kills the cells Gray This is why the percentage of alcohol in wines and beers is typically in this concentration range. However, like humans, different strains of yeast can tolerate different amounts of alcohol.
Therefore, brewers and wine makers can select different strains of yeast to produce different alcohol contents in their fermented beverages, which range from 5 percent to 21 percent of alcohol by volume. For beverages with higher concentrations of alcohol like liquors , the fermented products must be distilled. Today, beer brewing and wine making are huge, enormously profitable agricultural industries.
These industries developed from ancient and empirical knowledge from many different cultures around the world. Today this ancient knowledge has been combined with basic scientific knowledge and applied toward modern production processes. These industries are the result of the laborious work of hundreds of scientists who were curious about how things work.
Barnett, J. A history of research on yeast 1: Work by chemists and biologists, — Yeast 14 , — A history of research on yeast 2: Louis Pasteur and his contemporaries, — Yeast 16 , — A history of research on yeast 3: Emil Fischer, Eduard Buchner and their contemporaries, —
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