The production of alcoholic beverages from fermentable carbon sources by yeast is the oldest and most economically important of all biotechnologies. Yeast plays a vital role in the production of all alcoholic beverages. Yeast plays a vital role in the production of all alcoholic beverages and the selection of suitable yeast strains is essential not only to maximise alcohol yield, but also to maintain beverage sensory quality [ 2 ].
On the other hand, beers and ciders contain less amounts of ethanol with a balanced and distinctive sensory profile characteristic of each one. In recent years, new consuming trends and requirements for new and innovative products have emerged. This situation led to rethink about the existing fermented beverages and to meet the demands of consumers. Yeasts are largely responsible for the complexity and sensory quality of fermented beverages.
Based on this, current studies are mainly focused on the search of new type of yeasts with technological application. Non- Saccharomyces yeasts have always been considered contaminants in the manufacture of wine and beer.
Therefore, procedures for eliminating them are routinely utilized such as must pasteurization, addition of sulfite and sanitization of equipment and processing halls. In recent years, the negative perception about non- Saccharomyces yeasts has been changing due to the fact that several studies have shown that during spontaneous fermentations of wine, these yeasts play an important role in the definition of the sensory quality of the final product.
Based on this evidence, the fermentative behavior of some non- Saccharomyces yeasts is being studied in deep with the purpose of finding the most adequate conditions and the most suitable strain to be utilized in the production of fermented beverages. Beer is the most consumed alcoholic beverage worldwide. It is traditionally made from four key ingredients: malted cereals barley or other , water, hops, and yeast.
Each of these ingredients contributes to the final taste and aroma of beer. During fermentation, yeast cells convert cereal-derived sugars into ethanol and CO 2. At the same time, hundreds of secondary metabolites that influence the aroma and taste of beer are produced. Variation in these metabolites across different yeast strains is what allows yeast to so uniquely influence beer flavor [ 9 ]. Although most breweries use pure yeast cultures for fermentation, spontaneous or mixed fermentation is nowadays used for some specialty beers.
These fermentation procedures involve a mix of different yeast species and bacteria as well that contribute to the final product sequentially, giving the beer a high degree of complexity. Commonly, breweries have their own stock of selected yeasts for their specific beers. As it is well-known, two types of yeast are used in brewing: S. 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 ].
Although traditional ciders are produced from spontaneous fermentation of juice carried out by autochthonous yeasts, selected S. This ensures a consistent quality of the finished products [ 12 ]. Some other non- Saccharomyces yeast species are involved in spontaneous fermentation of apple juice for cider production. However, these yeasts contribute at a lesser extent than Saccharomyces and can be producers of off-flavours [ 13 ]. Research articles on this type of product are scarce compared to wine, especially in phenomena associated with microbial activities.
The microbiome of wine fermentation and its dynamics, the organoleptic improvement of healthy and pleasant products and the development of starters are now extensively studied. Although the two beverages seem close in terms of microbiome and process with both alcoholic and malolactic fermentations , the inherent properties of the raw materials and different production and environmental parameters make it worthwhile research on the specificities of apple fermentation.
An excellent review of the microbial implications associated with cider production, from ecosystem considerations to associated activities and the influence of process parameters [ 11 ]. In addition to these three worldwide-famous fermented beverages, there are many others made from fruit in various countries in Africa, Asia, and Latin America.
Although its consumption is local or regional, in some countries drinks made using fruits such as bananas or grapes as raw materials are very popular. The most widespread alcoholic fruit drink in Eastern Africa is banana beer, which in addition to gastronomic interest is especially culturally relevant.
Banana beer is a mixed beverage made from bananas and a cereal flour often sorghum flour [ 14 ]. Dates in North Africa, pineapples and cashew fruits in Latin America and jack fruits in Asia are other of the most relevant products.
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. The fermentation of the dough made by the yeasts is the most critical phase in the making of bread. The fermentative yield of yeast cells during this fermentation is crucial and determines the final quality of the bread.
Yeasts not only produce CO 2 and other metabolites that influence the final appearance of the dough, volume, and texture, and of course, the taste of the bread. The yeast strain, pregrowth conditions, its activity during the dough fermentation process, the fermentation conditions, as well as the dough ingredients are basic to control the process.
The fermentation rate is also conditioned by the ingredients of the dough, including the amounts of sugar and salt used in its preparation. Commercial bread producers currently produce various types of dough such as lean, sweet or frozen dough. Depending on the type of dough, and to obtain optimal fermentation rates, it is recommended to use suitable yeast strains with specific phenotypic traits [ 15 ].
Yeasts play an important role in coffee production, in the post-harvest phase. Its performance can be done in two phases. On the one hand, aerobically, in which the berries just collected are deposited in a tank and the yeasts are allowed to act. This process is carried out under control of basic parameters, such as time and temperature.
Alternatively, coffee berries are deposited in a container mixed with water and microorganisms are allowed to act anaerobically in the absence of oxygen. This second process is more homogeneous and easy to control than the aerobic. Sometimes, coffee beans are even fermented in a mixed process, first in an aerobic and finally anaerobic manner [ 16 ]. The process is naturally carried out by the yeasts present in the mixture, although the process can be improved by the addition of appropriate enzymes polygalacturonase, pectin lyase, pectin methylesterase [ 17 ].
Raw cacao beans have a bitter and astringent taste, because of high phenolic content. Anthocyanins are one group of these polyphenols, and it both contributes to astringency and provide the reddish-purple color. Fermentation allows the enzymatic breakdown of proteins and carbohydrates inside the bean, creating flavor development. This is aided by microbial fermentation, which create the perfect environment through the fermentation of the cacao pulp surrounding the beans.
This processing step enables the extraction of flavor from cacao and contributes to the final acidity of the final product. Yeasts and also bacteria ferment the juicy pulp among the cacao beans by different methods, generally following a an anaerobic phase and an aerobic phase. During the anaerobic phase, the sugars of the pulp sucrose, glucose, fructose are consumed by yeasts using anaerobic respiration to yield carbon dioxide, ethanol, and low amounts of energy [ 18 , 19 ].
The aerobic stage is dominated by lactic and acetic-acid-producing bacteria [ 20 ]. The fermentation processes of substrates such as xylose are also of high interest on an industrial level. In addition to expanding the range of substrates that can be used for this purpose, they allow the environmental cost of efficient production of biofuels and other advanced chemicals to be reduced.
Some interesting approaches have been made in biorefinery to reprogram yeast for use in these bioprocesses [ 21 , 22 , 23 ]. This issue in Microorganisms aims to contribute to the update of knowledge regarding yeasts, regarding both basic and also applied aspects. Among the great contributions to this issue we have a manuscript devoted to the brewing industry and the recent isolation of the yeast Saccharomyces eubayanus [ 24 ].
The use of headspace solid-phase microextraction followed by gas chromatography-mass spectrometry HS-SPME-GC-MS has contributed to the production of volatile compounds in wild strains and to compare them to a commercial yeast. All these findings highlight the potentiality of this yeast to produce new varieties of beers.
Haile et al. Almost 30 isolates, eight of them with the ability to produce pectinase enzymes were identified and confirmed by using molecular biology techniques. 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. Both alcoholic fermentation and glycolysis are anaerobic fermentation processes that begin with the sugar glucose. Glycolysis requires 11 enzymes which degrade glucose to lactic acid Fig. Alcoholic fermentation follows the same enzymatic pathway for the first 10 steps. The last enzyme of glycolysis, lactate dehydrogenase, is replaced by two enzymes in alcoholic fermentation.
These two enzymes, pyruvate decarboxylase and alcoholic dehydrogenase, convert pyruvic acid into carbon dioxide and ethanol in alcoholic fermentation. The most commonly accepted evolutionary scenario states that organisms first arose in an atmosphere lacking oxygen. There are several scientific difficulties, however, with considering fermentations as primitive energy harvesting mechanisms produced by time and chance.
Two ATPs are put into the glycolytic pathway for priming the reactions, the expenditure of energy by conversion of ATP to ADP being required in the first and third steps of the pathway Fig. A total of four ATPs are obtained only later in the sequence, making a net gain of two ATPs for each molecule of glucose degraded. The net gain of two ATPs is not realized until the tenth enzyme in the series catalyzes phosphoenolpyruvate to ATP and pyruvic acid pyruvate.
This means that neither glycolysis nor alcoholic fermentation realizes any gain in energy ATP until the tenth enzymatic breakdown. It is purely wishful thinking to suppose that a series of 10 simultaneous, beneficial, additive mutations could produce 10 complex enzymes to work on 10 highly specific substances and that these reactions would occur in sequence.
Enzymes are proteins consisting of amino acids united in polypeptide chains. Their complexity may be illustrated by the enzyme glyceraldehyde phosphate dehydrogenase, which is the enzyme that catalyzes the oxidation of phosphoglyceraldehyde in glycolysis and alcoholic fermentation. Glyceraldehyde phosphate dehydrogenase consists of four identical chains, each having amino acid residues.
The number of different possible arrangements for the amino acid residues of this enzyme is astronomical. To illustrate, let us consider a simple protein containing only aim acids. There are 20 different kinds of L-amino acids in proteins, and each can be used repeatedly in chains of Therefore, they could be arranged in 20 or 10 different ways.
Even if a hundred million billion of these 10 17 combinations could function for a given purpose, there is only one chance in 10 of getting one of these required amino acid sequences in a small protein consisting of amino acids. By comparison, Sir Arthur Eddington has estimated there are no more than 10 80 or 3, x 10 79 particles in the universe.
Even by most generous estimates, therefore, there is not enough time or matter in our universe to "guarantee" production of even one small protein with relative specificity.
If probabilities involving two or more independent events are desired, they can be found by multiplying together the probability of each event. Consider the 10 enzymes of the glycolytic pathway. And 1 in 10 1, is only the odds against producing the 10 glycoytic enzymes by chance. It is estimated that the human body contains 25, enzymes. If each of these were only a small enzyme consisting of amino acids with a probability of 1 in , the probability of getting all 25, would be 10 25, , which is 1 chance in 10 2,, The actual probability for arranging the amino acids of the 25, enzymes will be much slimmer than our calculations indicate, because most enzymes are far more complex than our illustrative enzyme of amino acids.
Mathematicians usually consider 1 chance in 10 50 as negligible. In our calculations, 10 was considered the total number of events that could occur within the time and matter of our universe. The chances for producing a simple enzyme-protein having amino acid residues was I in 10 The probability for 25, enzymes occurring by chance alone was 1 in 10 2,, It is preposterous to think that even one simple enzyme-protein could occur by chance alone, much less the 10 in glycolysis or the 25, in the human body!
There are still other problems with the theory of evolution for alcoholic fermentation and glycolytic pathways. It is necessary to account for the numerous complex regulatory mechanisms which control these chemical pathways. For example, phosphofructokinase is a regulatory enzyme which limits the rate of glycolysis.
Glycogen phosphorylase is also a regulatory enzyme; it converts glycogen to glucosephosphate and thus makes glycogen available for glycolytic breakdown. In complex organisms there are several hormones such as somatotropin, insulin, glucagon, glucocorticoids, adrenaline thyroxin and a host of others which control utilization of glucose.
No evolutionary mechanism has ever been proposed to account for these control mechanisms. In addition to the regulators, complex cofactors are absolutely essential for glycolysis.
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