Molds appeared on our planet about 200 million years ago. Mold can both take life and save from death. The mold looks beautiful, but at the same time it does not cause other feelings, except for disgust. Mold fungi are a variety of fungi that form branching mycelia without large fruiting bodies. Mold refers to micromycetes. These are fungi and mushroom-like, having microscopic dimensions. Mold fungi are widespread in nature, they develop almost everywhere. Large colonies grow on nutrient media at high temperature and high humidity, and mold growth is not limited, provided food is available. Mold fungi are unpretentious to the environment and food.
Fig.1. The structure of mycelium and vegetative organs of reproduction of mold fungi
1 - unicellular (mukor); 2 - multicellular (penicillium); 3 - a - penicillium conidiophore with conidia; b - Aspergillus conidiophore with conidia; c - sporangiophore mucor with sporangia filled with sporesIn the structure of mold fungi, branching hyphae forming a mycelium, or mycelium, are distinguished. Fungi related to molds are extremely diverse, but they all have typical features. The mycelium (mycelium) of mold fungi is the basis of their vegetative body and looks like a complex of branching thin filaments (hyphae). The hyphae of the fungus are located on the surface or inside the substrate on which the fungus has settled. In most cases, molds form large myceliums that occupy a vast surface. Lower fungi have a non-cellular mycelium, while in most mold fungi, the mycelium is divided into cells.
Reproduction of fungi
Fungi can reproduce different ways. The simplest, characteristic of all mushrooms, is reproduction by parts of the mycelium. Each part of the mycelium (mycelium), having got to a new area of the substrate, under favorable circumstances becomes independent and develops as a whole organism, and the part of the mycelium, which is immersed in the nutrient substrate, plays the main role in providing the mold fungus with nutrients, moisture and minerals. The air part, rising above the surface of the substrate, as a rule, serves to form various bodies, with the help of which mold fungi reproduce (oidia, spores, conidia, etc.).
Oidia are bodies that are parts of the mycelium. They are formed by some multicellular fungi, in which the mature mycelium breaks up into many small areas that acquire a dense shell.
Spores are bodies of various shapes, measuring up to several microns; usually found at the ends of the hyphae of the aerial part of the mycelium, inside special oval and semicircular formations - sporangia.
Angiospore spores are formed by the breakdown of the multinuclear cytoplasm of a young sporangium into many separate sections, which gradually become covered with their own membrane and turn into spores.
The filaments of aerial mycelium that carry sporangia are called sporangiophores. Such formation of spores is characteristic of unicellular fungi. In multicellular organisms, so-called exospores are formed, that is, external, or external, which are often called conidia, and the aerial hyphae that carry them are conidiophores. Conidia are formed by separation directly from conidiophores or special cells located at their top. These cells are usually oblong and are called sterigmata. Conidia are located on conidiophores (or on sterigmata) singly, in chains, etc.
Sporangiophores and conidiophores form a visible fluffy coating on the surfaces of materials affected by fungi. Its different color (green, black, olive, pink, white, gray, etc.) depends on the color of conidia, spores, oidia, which, when the fungi reach physiological maturity, are formed in huge quantities. Mushroom mycelium is usually colorless.
Many fungi, reproducing in one way or another vegetatively, under suitable developmental conditions, can also reproduce sexually. This process is different for different mushrooms. However, in this case, special fruiting bodies are always formed, in some cases reaching enormous sizes (cap, lamellar, tubular and other naturally occurring fungi are the fruiting bodies of mold fungi).
Sexual spores are located on plates or in receptacles - bags. An example of the latter are various types of raincoats, stitching. Mushrooms that can reproduce Chlamydospores and sclerotia of fungi sexually are called perfect. Some fungi do not reproduce sexually at all. They are classified as imperfect. Knowledge of the structural features of the mycelium, organs of vegetative reproduction, and the structure of fruiting bodies is necessary in practical work to recognize specific pathogens of certain processes.
Many fungi, when adverse conditions occur, are capable of forming resting stages in the form of so-called sclerotia. These are strong, hard on the surface, usually dark, and inside are white nodules of various sizes and shapes, formed from tightly intertwined hyphae. Sclerotium, falling into conditions favorable for development, germinate and form one or another (depending on the type of fungus) reproductive organs. They often form in the ears of cereals. Chlamydospores are another resting stage. During their formation, the cytoplasm inside the hyphae is collected in the form of lumps, forming a new shell, usually thick and colored, and the hyphae become like chains or rosaries, consisting of chlamydopores. Sometimes chlamydospores are formed only at the ends of the hyphae. The multicellular structure, the differentiation of vital functions between the parts of the fungus - aerial and deep mycelium - indicate that mold fungi are more highly organized, complex organisms compared to bacteria.
Mushroom nutrition
Fig.2. Molds Fungus aspergillus fumigatus
There are many types of mold found in nature, such as Penicillium spp, Mycorales, Aspergillus, Fusarium, Dematiaceae, Saccharomycetaceae, etc. Fungi of the genus Penicillum are of great importance to humans. Penicillium is a green mold that develops on plant substrates, including food. Penicillium produces the antibiotic penicillin, the world's first discovered antibacterial drug. It is also important for humans to use yeast related to Saccharomyces fungi in the household. Yeasts are fungi that do not form a classic mycelium, and their vegetative cells reproduce by budding or division. Yeast fungi can live as individual single cells throughout their life cycle. Since ancient times, yeast has been widely used by man, as these fungi are involved in the process of alcoholic fermentation. This property of yeast is used in the production of alcohol and alcohol-containing products, winemaking, baking, confectionery, production of feed protein for livestock nutrition.
Many types of mold fungi have pathogenic properties, that is, they can provoke diseases in humans, animals, and plants. Other types of mold harm the human economy, because they spoil food products, including vegetables and fruits, when long-term storage cause damage to timber and fabrics.
Yeast, their structure and reproduction
Yeasts are single-celled non-motile organisms. They can be of various shapes: elliptical, oval, spherical and rod-shaped. The length of the cells ranges from 5 to 12 microns, the width - from 3 to 8 microns. The shape and size of yeast cells are variable and depend on the genus and species, as well as on the cultivation conditions, the composition of the nutrient medium, and other factors. Young cells are more stable, so young cultures are used to characterize yeast. A yeast cell consists of a cell wall, an adjacent cytoplasmic membrane, cytoplasm or protoplasm, inside which are located organelles and inclusions (reserve substances) in the form of fat droplets, glycogen grains and volutin.
Fig.3. Scheme of the structure of a yeast cell
1 - fissile nucleus; 2 - glycogen; 3 - volutin; 4 - mitochondria
Yeasts belong to the class of marsupials (Ascomycetes - ascomycetes) to the subclass of the simplest marsupials (Protoascales - protoasks). The classification of yeast is based on the method of reproduction and some physiological characteristics. The main systematic feature is the ability to form spores. On this basis, yeasts are divided into two groups: sporogenic yeast - yeast capable of forming spores, and asporogenic yeast - not forming spores, that is, not having sexual reproduction.
According to some researchers, the second group of yeast should be attributed to the class of imperfect fungi (Fungi imperfecti - fungi imperfecti), although the loss of the ability to reproduce sexually is secondary, and they can also be classified as marsupial fungi. The classification of sporogenic fungi was proposed in 1954 by V. I. Kudryavtsev. It is based on the method of vegetative propagation. V. I. Kudryavtsev proposes to combine all yeasts into one order of unicellular fungi (Unicellomycetales - unicellomycetes).
He divides sporogenous yeasts into three families based on vegetative reproduction:
Family Saccharomycetaceae (saccharomycetace) - reproduce by budding. This family includes the genera Saccharomyces (saccharomyces), which has the greatest practical importance, Pichia (pichia), Hasenula (ganzenula), and others (17 genera in total). They differ in the form of spores and the way they form and germinate.
Family Schizosaccharomycetaceae (schizosaccharomycetace) - reproduce by division. This family includes two genera: Schizosaccharomyces (schizosaccharomyces) and Octosporomyces (octosporomyces).
Family Saccharomycodaceae (saccharomycodace) - reproduction begins with budding and ends with division. The main genera of this family are Saccharomycodes (saccharomycodes) and Hanseniaspora (ganzeniaspora).
Asporogenic yeasts are classified according to the system of J. Lodder and Kroeger van Rij, proposed in 1952. The classification is based on the ability of microorganisms to form false mycelium and the ability to ferment. The main genera of this group are Candida (Candida) and Torulopsis (Torulopsis).
Yeast can reproduce vegetatively (by budding or division) and with the help of spores. When budding, a tubercle appears on the mother cell - a kidney that grows and, having reached a certain size, separates from the mother cell. Under favorable conditions, the budding process lasts about 2 hours. In some yeasts, the daughter cells do not separate from the mother cells, but remain connected, forming a false mycelium (filmous yeast).
In most yeasts, under unfavorable conditions, for example, with a sharp transition from good food unfortunately, spore formation occurs, although there are asporogenic yeasts that never form spores (Candida, Torulopsis). Spores are mostly formed asexually, although the cell nucleus undergoes a reduction division before that, so that the spores have a haploid (single) set of chromosomes.
From 2 to 8 ascospores appear in the cell, which, when mature, can continue to multiply by budding, giving a weakened haploid generation. As a result of the fusion of two haploid ascospores, a diploid zygote is formed, which subsequently gives a normal generation. The formation of sexual spores is observed in the yeast Zigosaccharomyces (zygosaccharomyces). In them, the formation of spores is preceded by cell fusion (copulation).
The practical importance of yeast
The most important practical yeasts are Saccharomyces cerevisiae and Saccharomyces ellipsoideus. Yeast Sacch. cerevisiae may be round or oval in shape. Widely used in baking, brewing, kvass brewing and for the production of alcohol. Under the influence of environmental conditions, certain types of yeast acquired some isolated features. These types of yeast are called races. Various industries use their own races of yeast. The alcohol industry, for example, uses races XII, XV, II, Ya. M, and others. They have the ability to actively ferment sugar at a temperature of 28-30 ° C and are relatively resistant to alcohol. For the preparation of beer, races with slow fermentation at relatively low temperatures (4-10 ° C) are used, which give the drink an aroma, with a low alcohol content. In baking, races are used that have the speed of reproduction, fermentation energy and lifting power.
Yeast Sacch. ellipsoideus (Sacch. vini). This group of yeasts is ellipsoidal in shape. They are most often used in winemaking. There are several races with properties to give wines a characteristic taste and aroma (bouquet). Members of the yeast group Sacch. lactis cause alcoholic fermentation in fermented milk products.
Along with useful representatives, there are species from the genus Saccharomyces (for example, Sacch. Pasteurianum, Sacch. intermedius, Sacch. validus, Sacch. turbidans), which are pests of the brewing industry. When developing in beer, they give it an unpleasant taste and smell, the drink turns cloudy. The class Ascomycetes includes a number of yeasts and yeast-like organisms that have lost the ability to sporulate. Some of them cause spoilage of raw materials and finished food products.
Biotechnology is a newfangled word, but people learned to use microorganisms for their economic needs thousands of years ago. This, of course, is about yeast, without which neither winemaking, nor brewing, nor baking would be possible. So what is yeast? How were they "domesticated"? How are they produced industrially? And is it true that yeast bread is dangerous? Let's try to figure it out.
Yeast is produced in three types: traditional pressed (pictured), liquid suspension ( yeast milk) and dried. From the point of view of consumer properties, there is practically no difference between them, but Russian bakeries prefer liquid and pressed yeast, while dried ones are more convenient in everyday life.
Oleg Makarov
Take an unwashed plum or grape in your hand. See the white patch? Many microscopic sweet tooth are on the surface of the berries. In a certain phase of life, they are able to cause fermentation: eat sugar and release alcohol and carbon dioxide. Although we buy specially produced yeast for the needs of bakery, generally speaking, these microorganisms are by no means some kind of a rare species They exist in abundance around us.
Unrecognized life
If they were not so common, the fateful meeting of man with yeast might not have happened, and who knows how this would have affected the development of human civilization. And so, due to the fact that yeast lives both on cereals and on hop cones, beer has become one of the oldest food products- it was cooked, apparently, 10,000 years ago. Later, in the II millennium BC. appeared yeast dough. Both products of yeast metabolism came in very handy for mankind: alcohol became one of the oldest and most popular drugs in the world, and carbon dioxide saturated beer with bubbles and perfectly loosened the dough, giving it splendor and increasing it in volume.
As probably many people know, yeast is mushrooms, but mushrooms are unusual. Unlike fly agaric and russula, they do not form a specific vegetative body - mycelium - and exist in a single-celled form. In total, there are about 1500 types of yeast, and they belong to two large groups - ascomycetes and basidiomycetes.
The process of reproduction of yeast cells consists of several laboratory and industrial stages. From a 10 ml tube containing a small population of yeast cells surrounded by a sterile environment, several tens of tons of yeast are obtained as a result.
Using yeast for thousands of years, until relatively recent times, by historical standards, people did not even suspect what they were actually dealing with. Yeast was able to see through a microscope Anthony van Leeuwenhoek in 1680, but did not understand that he was living organisms. Only Louis Pasteur in 1857 managed to prove the connection between alcoholic fermentation and the vital activity of microscopic fungi.
All this, however, did not prevent the improvement of yeast cultures for thousands of years by preserving successful starter cultures. Spontaneous selection was replaced by directed selection (just after Pasteur's discovery), and today laboratories of scientific institutes and food companies are working on improving yeast strains.
Mushrooms in a jar
If only individual enthusiasts are engaged in winemaking and brewing at home, then baking with yeast happens from time to time in almost every home, which is why baker's yeast is the most interesting product for all of us. PM talked to Vitaly Vysotsky, director of the Voronezh yeast plant, part of the Lesaffre group, about how baker's yeast is developed and produced, as well as about some of the myths associated with it.
“The selection and research of yeast strains is carried out by a special scientific division of the Lesaffre group,” says Vitaly Vysotsky. - Some cultures can work well, for example, with sweet dough, others - with other types of test. Yeast cell strains reproduce in pure form. This is the know-how of the company, and their samples are stored at low temperatures in a special storage bank in the city of Marc-en-Barolles. It is from this storage that the group's enterprises receive test tubes containing a chilled sterile (that is, purified from other microorganisms) medium and only a few grams of yeast cells of an accurately identified type. Yeast production consists in the fact that, through several stages of reproduction, a small population of yeast cells from a test tube gives rise to yeast in commercial quantities (hundreds of tons).”
Forced to breed
A mushroom population undergoes several stages of reproduction. The first two are carried out under sterile laboratory conditions. First, 500 ml is obtained from 10 ml. Then from 500 ml - 10 liters of medium containing yeast cells.
These 10 liters already reach the production site. The initial stage consists in the production of a pure culture - the so-called mother yeast, the collection of which is already several hundred kilograms. Further, during the first generation and commercial generation, the yeast mass increases to several tens of tons.
Interestingly, the process of yeast production is in a kind of antiphase with respect to their practical application. “Yeast has both aerobic and anaerobic modes of life,” explains Vitaly Vysotsky. - In the absence of oxygen (as, for example, in a dough or liquid), the body of a yeast cell is aimed at survival, and not at reproduction. It is in this phase that the cell releases a large amount of alcohol and carbon dioxide, so the anaerobic method is really useful for us. However, in the production of yeast, it is necessary for the cells to actively multiply, and for this they need not only nutrients but also oxygen.
Yeasts, in particular fungi from the Saccharomyces family, which are used in baking, reproduce vegetatively by budding. First, an outgrowth appears on the mother cell, then mitotic division of the nucleus occurs, the formation of a cell wall and separation of cells from each other. The mother cell is scarred by budding, which makes it possible to determine its age. Usually, the mother cell can form 20-30 buds.
The production process is the creation and control of favorable conditions for the reproduction of yeast. These conditions are the presence of sufficient nutrition and access to oxygen. The main food sources for yeast are easily digestible sugars, i.e. glucose, maltose, sucrose, galactose. Also needed minerals, vitamins, so that the cell has everything necessary for the construction of the kidney.
Therefore, for the production of yeast, it is necessary to prepare a nutrient medium, place the yeast in it, and, as the yeast absorbs substances from the nutrient medium, add nutrition and blow through this whole mass with atmospheric oxygen. When the mass fills the entire container, the process must be stopped and separation should be carried out - to separate the yeast cells from the medium. After that, only the process of forming the final product remains.
The traditional end product in Russia, and indeed in the world, is pressed yeast. As a rule, these are briquettes consisting of yeast cells, purified from the medium where they grew, and passed through special washing and filtration in vacuum filters. The briquetted yeast contains 32% yeast cells and 68% water.
Yeast is available in three types: traditional pressed (pictured), liquid suspension (yeast milk) and dried. From the point of view of consumer properties, there is practically no difference between them, but Russian bakeries prefer liquid and pressed yeast, while dried ones are more convenient in everyday life.
In the production of dried granular yeast, the propagation technology is similar, however, other strains are used - those that are more resistant to the final stage of production - drying. Drying (dehydration) is an extreme effect on the cell, and not all cultures are able to withstand it. The product goes through the stage of compressed yeast, which is then extruded through the extruder in thin "noodles". After that, they are finely chopped and sent to the dryer. There, the yeast is dehydrated with the help of forced warm air. This completes the process, the product is ready for packaging.
Yeastless mythology
The specificity of the modern information field is such that so-called horror stories are often used as a tool to attract the attention of the public. The calculation is made on the fact that fear is exactly the emotion that will make a person highlight this or that news in an endless and saturated information flow. Revelations about the dangers of certain foods are especially popular. People are scared by genetically modified vegetables and fruits, preservatives and flavorings. This series also includes ordinary baker's yeast, which allegedly damages the intestinal microflora, getting inside our body along with bakery products.
One of the myths is related to the so-called thermophilic yeast, which, they say, can survive the temperature of baking and then enter our digestive system alive. As an alternative, various types of yeast-free starters are offered. As usual, the source of this kind of "hypothesis" is not biologists and production workers, but some enthusiasts " healthy eating» different professions.
Lesaffre group experts consider all these arguments unprofessional and ridiculous. First, there are no “thermophilic yeasts” that can survive baking in nature. By the end of baking in the center of the crumb of a bakery product, the temperature reaches +96−98°C. At a temperature of +50°, inhibition of the vital activity of yeast cells begins, and at +55°, the protein in them is denatured and the yeast cells die.
Secondly, it is impossible to avoid getting live yeast into the body. As already mentioned, yeast is not only sold in stores, but also lives around us. Microscopic fungi are sure to be eaten by us along with fruits and other plant foods. There is, for example, a “folk” alternative to store-bought yeast in the form of plain water infused with raisins. In fact, this alternative is imaginary, since purchased yeast is replaced by the same yeast, only of other species that inhabit the surface of dried grapes. By the way, if you simply combine flour with water, replace the dough and put it in heat, after a while yeast fermentation will still begin there, because flour contains many microorganisms, including yeast cells. Another thing is that cultural strains that have undergone directed selection will give a predictable result, but other types of yeast taken from environment, especially in combination with other microorganisms, can give the dough undesirable taste and organoleptic qualities.
Thirdly, if we do not talk about purely chemical dough leavening agents, then the proposed biological yeast-free starter cultures are not 100% such. Indeed, in baking, for example, in the manufacture of rye bread, have long been used starter cultures based on lactic acid bacteria. But in reality, they are a symbiosis of bacteria and the same yeast cells. lactic acid bacteria By themselves, they cannot provide sufficient gas formation to quickly saturate the dough with carbon dioxide.
Dry or wet?
The last question we asked the director of the Voronezh Yeast Plant was probably asked by all home bakers more than once. What is the difference between pressed (wet) yeast and dried yeast, which are produced not in briquettes, but in small granules?
“From the point of view of consumer properties, there is no difference, and we produce yeast in all forms,” says Vitaly Vysotsky. But there is a technological difference. For old bakery enterprises, pressed yeast is preferable, since it is under them that the technology of their work is built. The main disadvantage of pressed yeast is the need to store it at a low temperature, in the range from 0 to +4°C. At higher temperatures, the cells enter the active phase, vital processes begin, which leads to a further increase in the temperature of the briquette. Dried yeast has a longer shelf life, and they do not need to create conditions - they are perfectly stored at room temperature. In addition, they are usually packaged in small packages, which is much more convenient in everyday life.
Under natural conditions, yeast is usually located on the surface of vegetables, fruits, in flower nectar and in stale foliage. Also, yeast is often found in the intestinal environment of many animals and humans.
Yeast composition
The cell consists of ¾ water, about half of it binds organelles, and ¼ is the liberated part. Based on age and general condition, we can indicate the approximate composition of dry cell matter:
- Nitrogen - 43-60%;
- Sugar - 16-39%;
- Fat - 2-14%;
- Minerals - 6-12%.
In addition to the main components, the cell also contains the content of important elements for metabolism - vitamins and enzymes.
Cell structure
The shape of the cell is varied, it can be spherical, elliptical or rod-shaped. Dimensions depend on the habitat and its conditions. Characteristics of yeast produced by the properties of younger yeast.
Yeast cells are composed of the following components:
- Cytoplasm;
- Core;
- Membrane;
- Mitochondria;
- Glycogen;
- Golgi apparatus;
- Ribosomes.
Breath
Oxygen is vital for the respiratory activity of yeast cells. But if necessary, yeast can completely do without it for some time.
Yeast Nutrition
Most of the species for energy in the process of nutrition use components of organic origin. In the absence of oxygen in the medium, yeast cells more often use various carbohydrates. In an environment enriched with oxygen, more types of substances are available for synthesis.
Yeast waste products
Yeast cells in the process of synthesis produce several types of alcohols, as well as various fatty acids. In addition, yeast cells have the ability to release certain substances into the environment, such as aldehydes and fusel oils.
reproduction
Yeast cells usually reproduce vegetatively by budding or division. There are known cases of sexual reproduction in some yeasts. In addition, there are yeast cells that form mycelium, which subsequently breaks up into individual arthrospores.
Yeast cell growth
Yeast growth is determined by the influence of environmental factors - temperature and humidity, acidity and atmospheric pressure. Favorable for enhanced growth is the average temperature.
Benefits of Yeast Organisms
Yeast is widely used not only in the food industry, in the production of bakery products and drinks, but also in the production of many useful elements- vitamins, polysaccharides, organic acids, enzymes and carotenoids.
The use of yeast cells in pharmacology and medicine
Biotechnologists use yeast cells in the production of many drugs. It is useful to use brewer's yeast in the treatment and prevention of allergic reactions. Cosmetologists recommend using them to strengthen general condition body and skin.
There is also a type of yeast that normalizes the functioning of the intestines and restores the microflora of the stomach. These yeast organisms help fight diarrhea and irritable bowels.
(yeast mushrooms)
fungi yeast - a type of fungus
✎ What are yeast fungi?
Mushroom yeast (yeast mushrooms) is a non-taxonomic position of unicellular fungi from the group of imperfect fungi that have lost their classical (mycelial) structure due to the transition of their habitat to liquid or semi-liquid, rich in organic substances, substrates.
They unite approximately 1,500 species, which belong mainly to the class of ascomycetes and less often to basidiomycetes.
✎ Features of Mushroom Yeast
Mushroom yeast(not to be confused with thermophilic yeast) is such a prefabricated type of fungus that does not have a typical mycelium and exists in the form of divided budding or dividing cells. They exist throughout their life, or most of it, in the form of completely separate single cells. And, due to their unicellular structure, they have a much higher metabolic rate than ordinary mycelial species, due to the relatively larger surface area of \u200b\u200btheir cells. Therefore, they grow and multiply always at an incredible rate.
Historically, such species have always been studied separately from others, due to the fact that the methods of their identification were more similar to bacteriological than mycological. Well, according to the ability of sexual reproduction, these species are divided into subgroups located in different classes of fungi:
in the class Ascomycetes and Basidiales these are:
- tubular,
- lamellar,
in the class of deuteromycetes, in which the sexual cycle is not found, these are:
- pycnidal,
- melanconial,
- hyphomycetes.
✎ How are yeast fungi arranged?
The body of yeast fungi is very different from all the others due to the fact that it consists of only one cell and therefore does not form mycelium (mycelium). And their reproduction is a very interesting phenomenon. A small protrusion appears on the cell, which grows, forming the so-called kidney and gradually turns into an independent cell, which is able to separate and, ultimately, separates. This process is called budding.
✎ The role of yeast in nature and everyday life
Mankind has long used yeast mushrooms in baking and cooking. alcoholic beverages. In many languages of the world, their name is associated with the fermentation process that they cause. Their Russian name comes from the word "shiver" and it accurately characterizes the state of the fermented wort or rising dough.
As already noted, about 1,500 species of imperfect fungi are known in nature, and we encounter many of them in everyday life. They are divided into:
- bakery,
- beer,
- wine.
For example, in baking, baker's yeast is used to make the dough rise and baking become "fluffy", while in winemaking and brewing, wine and brewer's yeast are used, respectively, for the fermentation process. Thus, an indisputable fact becomes obvious: yeast mushrooms were, are and will be constant companions and friends of man.
According to the classification, yeasts belong to the microscopic fungi of the kingdom Mycota. They are unicellular immobile microorganisms of small size - 10-15 microns. Despite the outward resemblance of yeast to large species of bacteria, they are classified as fungi due to their cell ultrastructure and methods of reproduction.
Rice. 1. View of yeast on a Petri dish.
Often in nature, yeasts are found on substrates rich in carbohydrates and sugars. Therefore, they are found on the surface of fruits and leaves, berries and fruits, on wound juices, in the nectar of flowers, in dead plant mass. In addition, they are found in soils (as an example, in litter), water. Yeast organisms of the genera Candida or Pichia are often found in the intestinal environment of humans and many animal species.
Rice. 2. Habitat for yeast.
The composition of yeast cells
All yeast cells contain about 75% water, 50-60% is bound intracellular, and the remaining 10-30% is released. The dry matter of the cell, depending on age and condition, on average contains:
- nitrogen 45-60%;
- sugar 15-40%;
- fat 2.5-13%;
- minerals 7-11%.
In addition, cells include a number of important components necessary for their metabolism - enzymes, vitamins. Yeast enzymes are catalysts different types fermentation and respiratory processes.
Rice. 3. Cells of yeast organisms.
Yeast cells have different shapes: ellipses, ovals, sticks, balls. The dimension is also different: often the length is 6-12 microns, and the width is 2-8 microns. It depends on the conditions of their habitat or cultivation, nutritional components and environmental factors. Young yeasts are the most stable in their properties, therefore, the characteristics and description of the species are carried out precisely on them.
Yeast organisms have all the standard components found in eukaryotic cells. However, in addition to this, they have unique distinctive properties of fungi and combine the features of the cellular structures of plants and animals:
- the walls are rigid, like in plants,
- there are no chloroplasts and there is glycogen, like in animals.
Rice. 4. Variety of yeast species: 1 - baker's yeast (Saccharomyces cerevisiae); 2 - the most beautiful mechnikovia (Metschnikowia pulcherrima); 3 - candida earthen (Candida humicola); 4 - sticky rhodotorula (Rhodotorula glutinis); 5 - red rhodotorula (R. rubra); 6 - golden rhodotorula (R. aurantiaca); 7 - Debaryomyces Cantarelli (Debaryomyces cantarelli); 8 - Cryptococcus Laurel (Cryptococcus laurentii); 9 - oblong nadsonia (Nadsonia elongata); 10 - pink sporobolomyces (Sporobolomyces roseus); 11 - sporobolomyces holsaticus (S. holsaticus); 12 - rhodosporidium diobovatum (Rhodosporidium diobovatum).
- core;
- Golgi apparatus;
- Cell mitochondria;
- ribosomal apparatus;
- fat inclusions, glycogen grains, and currency.
Some species contain pigments. In young yeasts, the cytoplasm is homogeneous. In the process of growth, vacuoles (containing organic and mineral components) appear inside them. In the process of growth, the formation of granularity is observed, an increase in vacuoles occurs.
As a rule, the shells include several layers with included polysaccharides, fats and nitrogen-containing components. Some of the species have a mucus membrane, so often the cells are glued together and form flakes in liquids.
Rice. 5. Cell structure of yeast organisms.
Respiratory processes in yeast
Yeast cells require oxygen for respiration, but many species (facultative anaerobic) can get by temporarily and without it, and receive energy from fermentation processes (oxygen-free respiration), while forming alcohols. This is one of their main differences from bacteria:
among yeast there are no representatives capable of living absolutely without oxygen.
The processes of respiration with oxygen are more energetically favorable for yeast, therefore, when it appears, the cells complete fermentation and switch to oxygen respiration, while releasing carbon dioxide, which contributes to faster cell growth. This effect is called Pasteur. Sometimes, with a high glucose content, the Crabtree effect is observed, when even if there is oxygen, the yeast cells ferment it.
Rice. 6. Respiration of yeast organisms.
What do yeast eat
Many yeasts are chemoorganoheterotrophic and use organic nutrient components to obtain energy for nutrition and energy.
In oxygen-free conditions, yeast prefers to use carbohydrates such as hexose and oligosaccharides synthesized from it for their nutrition. Some species can also absorb other types of carbohydrates - pentose, starch, inulin. With access to oxygen, they are capable of consuming a wider range of substances, including fatty, hydrocarbon, alcohol and others. Such complex types of carbohydrates, such as, for example, lignins and celluloses, are not available to them for assimilation. Nitrogen sources for them, as a rule, are ammonium salts and nitrates.
Rice. 7. Yeast under a microscope.
What do yeast synthesize
Most often, yeasts produce various types of alcohols during metabolism - most of them are ethyl, propyl, isoamyl, butyl, isobutyl types. In addition, the formation of volatile fatty acids was found, for example, the synthesis of acetic, propionic, butyric, isobutyric, isovaleric acids was revealed. In addition, during their vital activity, they can release a number of substances into the environment in small concentrations - fusel oils, acetoins, diacetyls, aldehydes, dimethyl sulfide and others. It is with such metabolites that the organoleptic properties of the products obtained by using them are often associated.
Yeast propagation processes
A distinctive feature of yeast cells is their ability to reproduce vegetatively, when compared with other fungi, which occurs both from the budding of spores or, for example, zygotes of cells (such as the genera Candida or Pichia). Some yeasts can realize the processes of sexual reproduction containing mycelial stages, when the formation of a zygote and its further transformation into a “bag” of spores is observed. Some yeasts that form mycelium (for example, the genera Endomyces or Galactomyces) are capable of disintegrating into individual cells - arthrospores.
Rice. 8. Reproduction of yeast.
What does yeast growth depend on?
The growth processes of yeast organisms depend on various environmental factors - temperature, humidity, acidity, osmotic pressure. Most yeast prefer medium temperature, and there are practically no extremophile species among them that prefer too high or, on the contrary, low temperature. The existence of species capable of enduring adverse environmental conditions is known. Antibiotics can be used to suppress the growth and development of some yeast organisms.
Rice. 9. Production of yeast.
What are the benefits of yeast
Often yeast is used in the household or industry. Man has long begun to use them for his life, for example, in the preparation of bread and drinks. Today, their biological abilities are used in the synthesis of useful substances - polysaccharides, enzymes, vitamins, organic acids, carotenoids.
Rice. 10. Wine is a product obtained through the activity of yeast.
The use of yeast in medicine
Yeast is used in biotechnological processes in the production of medicinal substances - insulin, interferon, heterologous proteins. Doctors often prescribe brewer's yeast to weakened people with allergic diseases. They are also used for cosmetic purposes to strengthen hair, nails, improve skin condition.
Rice. 11. Yeast in cosmetology.
In addition, there are yeast species (for example, Saccharomyces boulardii) that are able to maintain and restore the microflora of the gastrointestinal tract, as well as relieve the symptoms and risk of diarrhea and reduce muscle contractions in patients with irritable bowel syndromes.
Are there harmful yeasts?
It is known that the reproduction of yeast in food products can cause spoilage (for example, swelling processes, changes in odors and tastes occur). In addition, according to mycologists, among them are pathogenic, capable of causing various disorders of living organisms, as well as a number of serious diseases of people who have weakened immunity.
Human diseases include, for example, candidiasis caused by the yeast Candida and cryptococcosis, which is caused by Cryptococcus neoformans. It has been shown that these pathogenic yeast species are often normal inhabitants of the human microflora and begin to multiply actively precisely when they are weakened, when they receive various injuries, when burns occur, after surgical interventions, when taking antibiotics for a long time, sometimes in small or, on the contrary, elderly people.
