Mother bacteria are unicellular eukaryotic microorganisms, which are ubiquitous in nature and mainly distributed in acidic environments with high sugar content, such as fruits, vegetables, nectar and plant leaves, as well as orchard soil. Petroleum yeast is mainly distributed in the soil around the oil field. Most yeasts are saprophytic. The optimum growth temperature is 25~30℃. There are several kinds of yeasts commonly used in industry:
1, Saccharomyces cerevisiae.
Beer yeast is a widely used strain in the genus Saccharomyces.
Beer yeast cells grown on wort medium are round, oval or oval. Cells are solitary, paired or strung or clustered. The size of yeast cells is about 5 ~10× 6 ~12 μ m and 3 ~ 9× 4.5 ~10 μ m.
The cell length-width ratio is about 1~2.
According to the aspect ratio of beer yeast cells, they can be divided into three groups: the first group of cells are mostly round and oval, and the aspect ratio is 1~2. This kind of yeast is mainly used to produce beer, liquor, alcohol and bread. In the second group, most cells are oval or rectangular, and the length-width ratio is 2. Including some varieties of beer yeast, such as wine yeast and other strains, generally used in the production of wine and fruit wine. The cells of the third group of yeast are rectangular, and the aspect ratio is greater than 2. This group of yeasts is resistant to high osmotic pressure and can be used to ferment sugarcane molasses to produce alcohol.
On wort agar medium, the colonies were white, shiny, flat and tidy. There are two growth behaviors in liquid medium. In industry, yeast with high fermentation degree and not easy to agglutinate and precipitate is called upper yeast. Yeast that is easy to agglutinate and precipitate and has low fermentation degree is called the following yeast.
The asexual reproduction of beer yeast is budding, and sexual reproduction can form ascospores. Generally, there are 1 4 round and oval smooth-surfaced ascospores in each ascocarp.
Beer yeast can ferment glucose, sucrose, maltose and galactose, but it can't ferment lactose and melibiose. Only about 1/3 raffinose can be fermented. Ammonium sulfate can be used as nitrogen source, but potassium nitrate cannot be used.
Beer yeast is widely used in traditional fermentation industries, such as beer, liquor, fruit wine, alcohol, medicinal yeast tablets, bread making and so on, so it is also called Saccharomyces cerevisiae. In recent years, Saccharomyces cerevisiae has also extracted nucleic acid, ergosterol, cytochrome C, clot and coenzyme A. Beer yeast, as a single cell protein (SCP), can be used as food, medicine and feed yeast because of its high content of vitamins and protein. Its invertase can be used to convert sucrose and make alcoholic chocolate. Beer yeast is often used to determine the contents of biotin, pantothenic acid, thiamine and inositol in microbial determination of vitamins.
2. Grape juice yeast (Saccharomyces cerevisiae)
Cultured in wort at 25℃ for 3 days, the cells were in the shape of figures, ovals, ovoids or sausages. On wort agar medium, the colonies were milky white, smooth, shiny and neat.
It can produce ascospores, and each ascospore has 1 and 4 spores. Spores are round or oval with smooth surface. The strain has strong fermentation ability, and turbidity often occurs in liquid culture.
Grape juice yeast is similar to Saccharomyces cerevisiae. The main difference is that it can ferment raffinose and melibiose. Grape juice yeast can also ferment glucose, sucrose, maltose and galactose. Can't ferment lactose. Ammonium sulfate can be used instead of potassium nitrate. Grape juice yeast is often used in the bottom fermentation of beer brewing, and can also be used as food and medicine.
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Classification of industrial yeast
Mother bacteria are unicellular eukaryotic microorganisms, which are ubiquitous in nature and mainly distributed in acidic environments with high sugar content, such as fruits, vegetables, nectar and plant leaves, as well as orchard soil. Petroleum yeast is mainly distributed in the soil around the oil field. Most yeasts are saprophytic. The optimum growth temperature is 25~30℃. There are several kinds of yeasts commonly used in industry:
1, Saccharomyces cerevisiae.
Beer yeast is a widely used strain in the genus Saccharomyces.
Beer yeast cells grown on wort medium are round, oval or oval. Cells are solitary, paired or strung or clustered. The size of yeast cells is about 5 ~10× 6 ~12 μ m and 3 ~ 9× 4.5 ~10 μ m.
The cell length-width ratio is about 1~2.
According to the aspect ratio of beer yeast cells, they can be divided into three groups: the first group of cells are mostly round and oval, and the aspect ratio is 1~2. This kind of yeast is mainly used to produce beer, liquor, alcohol and bread. In the second group, most cells are oval or rectangular, and the length-width ratio is 2. Including some varieties of beer yeast, such as wine yeast and other strains, generally used in the production of wine and fruit wine. The cells of the third group of yeast are rectangular, and the aspect ratio is greater than 2. This group of yeasts is resistant to high osmotic pressure and can be used to ferment sugarcane molasses to produce alcohol.
On wort agar medium, the colonies were white, shiny, flat and tidy. There are two growth behaviors in liquid medium. In industry, yeast with high fermentation degree and not easy to agglutinate and precipitate is called upper yeast. Yeast that is easy to agglutinate and precipitate and has low fermentation degree is called the following yeast.
The asexual reproduction of beer yeast is budding, and sexual reproduction can form ascospores. Generally, there are 1 4 round and oval smooth-surfaced ascospores in each ascocarp.
Beer yeast can ferment glucose, sucrose, maltose and galactose, but it can't ferment lactose and melibiose. Only about 1/3 raffinose can be fermented. Ammonium sulfate can be used as nitrogen source, but potassium nitrate cannot be used.
Beer yeast is widely used in traditional fermentation industries, such as beer, liquor, fruit wine, alcohol, medicinal yeast tablets, bread making and so on, so it is also called Saccharomyces cerevisiae. In recent years, Saccharomyces cerevisiae has also extracted nucleic acid, ergosterol, cytochrome C, clot and coenzyme A. Beer yeast, as a single cell protein (SCP), can be used as food, medicine and feed yeast because of its high content of vitamins and protein. Its invertase can be used to convert sucrose and make alcoholic chocolate. Beer yeast is often used to determine the contents of biotin, pantothenic acid, thiamine and inositol in microbial determination of vitamins.
2. Grape juice yeast (Saccharomyces cerevisiae)
Cultured in wort at 25℃ for 3 days, the cells were in the shape of figures, ovals, ovoids or sausages. On wort agar medium, the colonies were milky white, smooth, shiny and neat.
It can produce ascospores, and each ascospore has 1 and 4 spores. Spores are round or oval with smooth surface. The strain has strong fermentation ability, and turbidity often occurs in liquid culture.
Grape juice yeast is similar to Saccharomyces cerevisiae. The main difference is that it can ferment raffinose and melibiose. Grape juice yeast can also ferment glucose, sucrose, maltose and galactose. Can't ferment lactose. Ammonium sulfate can be used instead of potassium nitrate. Grape juice yeast is often used in the bottom fermentation of beer brewing, and can also be used as food, medicine or feed.
3. Hansenula.
The vegetative cells of this genus are various in shape, including round, oval, oval and sausage. Multilateral bud. Some species can form pseudohyphae.
The shape of the ascus is the same as that of the vegetative cell. There are 1 and 4 ascospores, which are hat-shaped, Saturn-shaped, round and semicircle with smooth surface.
Hansenula anomalosa var. anomalosa. Anomalosa is a common species in Hansenula. The cells are round with a diameter of 4 ~ 7 μ m. There are sausages, ranging from 2.5 to 6× 4.5 to 20 μ m, and sausages as long as 30 μ m, which germinate multilaterally and can directly form ascomycetes from cells. Each ascomycete has 1 and 4 ascomycetes, but most of them have 2. Ascomycetes are hat-shaped and usually do not spread after being released from Ascomycetes. The colony of this variety growing on the inclined plane of wort agar is flat, milky white, dull and filamentous. After being cultured in wort, tremella fuciformis appeared on the wave surface, the culture solution became turbid, and bacteria were deposited at the bottom. Lactose and melibiose cannot be fermented. Maltose and galactose fermentation is weak or not acidic. It can assimilate nitrate and oxidized hydrocarbons, and can use kerosene as carbon source.
The yeast of this genus can produce ethyl acetate, thus increasing the flavor of the product, which can be used in wine making and food industry. However, they are harmful bacteria in alcohol production, because they can use alcohol as carbon source and produce dry wrinkles on the surface of drinks.
4. Coccidiosis
The cells of pseudosaccharomyces globosa are spherical, and the formation of eggs is slightly longer. Multilateral budding propagation.
On the wort slope, the colonies are milky white, with wrinkled and dull surface and neat or irregular edges. In liquid culture medium, precipitation and yeast ring appear, and sometimes fungi can also be produced.
This kind of yeast has certain economic significance. Some species can produce glycerol, erythritol, D- arabinitol and sometimes mannitol in different proportions. Under suitable conditions, 40% glucose can be converted into polyols. Others can produce organic acids, oils and fats. Some can use hydrocarbons to produce protein. ,
The strain has weak alcohol fermentation ability, which can produce ethyl acetate (different from strain to strain) and increase the flavor of liquor and soy sauce.
5. Candida
Cells are round, oval or oblong. Multilateral budding propagation. Will form pseudohyphae. The colonies on wort agar medium are milky white, smooth and shiny, with neat edges or hyphae. Liquid culture can form a floating membrane.
It can ferment glucose, sucrose and raffinose. Maltose, galactose, lactose and melibiose cannot be fermented. Does not decompose fat. Can assimilate nitrate.
The content of protein and vitamin B in Candida is higher than that in Saccharomyces cerevisiae. It can grow with urea and nitrate as nitrogen sources, and no other factors are added to the culture medium. It can make use of sulfurous acid waste liquid in paper industry, and can also make use of molasses, potato starch and wood hydrolysate. Therefore, Candida can be used to treat industrial and agricultural by-products and produce edible protein, which has important comprehensive utilization value. Some bacteria in this genus can convert 50% sugar into glycerol.
Candida is also a lipase-producing bacterium, which can be used for degreasing silk spinning raw materials in industry.
6. Pichia pastoris.
Cells are oval, rectangular or sausage-shaped, single-chain or short-chain. Heterotypic combination forms ascospores. Cryptosporidium is oval. On wort agar, the colonies were milky white and dull, with fine gaps at the edges. Cultured in wort, there are white wrinkled mushrooms on the surface of the culture solution and bacterial precipitation at the bottom.
This strain has weak ability to decompose sugar and does not produce alcohol. It can oxidize alcohol and resist high or high concentration alcohol. Wine and soy sauce often produce white flowers and form floating films, which are harmful bacteria in the brewing industry, such as Pichia farinosa.
7. Rhodotorula
Cells are round, oval or oblong. Multilateral bud with obvious red or yellow pigment. The capsule forms a variety of mucus colonies. There are good lipid-producing strains in this genus, which can extract a lot of fat from bacteria. Some species have weak oxidation effect on hydrocarbons and can synthesize β -carotene rope. Such as Rhodotorula glutinis var. Gelatin can oxidize alkanes to produce fat, and its content can reach 50 ~ 60% of dry biomass. Under certain conditions, it can also produce α -alanine and glutamic acid, and its ability to produce methionine is also very strong, reaching 1% of dry biomass.
8. Trichosporon gossypii
Also known as cotton cysticercosis. The culture effect was good at 26℃ on wort and Liu Ling medium. At first, wet creeping hyphae spread and grew; The colony is colorless or gray-white. Because riboflavin diffuses around the colony, it turns pale yellow after 2-3 days, lemon orange after 5 days, and yellow-green after 7- 10 days. Biotin is an important factor to promote the growth of the strain, and glycine can promote the production of riboflavin. It is reported that lard or corn oil can replace all carbon sources to cultivate the strain. And grow well;
Cotton cysticercosis can harm many important cash crops, such as cotton, citrus and tomato. It was originally isolated from infected cotton peaches. The strain has the ability to synthesize riboflavin in large quantities, and the yield can reach 4 187μ g/m 1, so it is an important strain for riboflavin production.
9. Geotrichum candidum
Geotrichum candidum is a common species in Geotrichum. Schizophrenia. Arthrospores are single or linked into chains, long cylindrical, square or oval, with blunt ends. Most of the arthrospores are 4.9 ~ 9.6× 5.4 ~16.6 μ m.
Culture in wort at 28~30℃ for one day to produce white pu. Plush or powdery, tough or fragile, true hyphae. The growth temperature is 33~37℃. The fermentation of glucose, mannose and fructose is weak. Can assimilate glycerol and ethanol; Sorbitol and mannitol. Can decompose pectin, grease, etc. Different nitrates. Bacterial cells are rich in protein, fat, vitamins and a lot of nucleic acids. It has the characteristics of strong adaptability, fast growth, large yield and simple cultivation method.
Geotrichum candidum has high nutritional value in protein, which can be used in food and feed, and can also be used to extract nucleic acid, so it has great value in comprehensive utilization of wastewater. In the process of koji-making, the pollution of Geotrichum candidum will reduce the fermentation ability and directly affect the liquor yield, which is a harmful bacterium in liquor production.