How to cultivate yeast
nutrition
Yeast, like other organisms, needs similar nutrition. Like bacteria, it has a set of intracellular and extracellular enzyme systems, which are used to break down macromolecules into small molecules that are easily metabolized by cells. It belongs to heterotrophs.
acidity
Yeast can grow in the range of PH 3.0 ~ 7.5, and the optimum PH is 4.5 ~ 5.0.
moisture
Like bacteria, yeast must have water to survive, but yeast needs less water than bacteria. Some yeasts can grow in an environment with little water, such as honey and jam, which shows that they have high tolerance to osmotic pressure.
temperature
Generally, yeast cells cannot grow at a temperature lower than the freezing point of water or higher than 47℃, and the optimum growth temperature is generally 20 ~ 30℃.
oxygen
Yeast can grow in aerobic and anaerobic environments, that is, yeast is facultative anaerobic bacteria. Under aerobic conditions, it decomposes sugar into carbon dioxide and water, and yeast grows faster. In the absence of oxygen, yeast breaks down sugar into alcohol and carbon dioxide.
use
The most commonly mentioned yeast is Saccharomyces cerevisiae, which has been used by humans to ferment bread and wine for thousands of years. During the fermentation of bread and steamed bread, the dough will release carbon dioxide.
Yeast is a simple single-celled eukaryote, which is easy to cultivate and grows rapidly, so it is widely used in modern biological research. As an important model organism, Saccharomyces cerevisiae is also an important research material in genetics and molecular biology.
Yeast contains circular DNA-plasmid, which can be used as a carrier of genetic engineering.
Use of yeast
eat
Dry yeast powder or granular products, which have no fermentation and reproduction ability, are for human consumption. It can be obtained by recycling yeast mud from brewery or by special cultivation and drying according to the requirements of human nutrition. The United States, Japan and some European countries add about 5% edible yeast powder to common foods such as bread, cakes, biscuits and scones to improve the nutritional value of food. Yeast autolysate can be used as an additive for meat, jam, soup, cheese, bread, vegetables and condiments. It is used as a food nutrition enhancer in baby food and health food. 5? Made from yeast autolysis extract? Nucleotide combined with monosodium glutamate can be used as additives to enhance food flavor. The concentrated invertase extracted from yeast is used as liquefier for chocolate with square eggs. Extracting lactase from yeast produced in whey can be used to increase sweetness in milk processing, prevent lactose crystallization in whey concentrated solution, and meet the needs of lactose intolerant consumers.
officinal
The manufacturing method and properties are the same as those of food yeast. Because it is rich in protein, vitamins, enzymes and other physiological active substances, it is made into yeast tablets, such as raw mother tablets, to treat indigestion caused by unreasonable diet. People with weak constitution can regulate metabolic function to some extent after taking it. In the process of yeast culture, if some special elements are added to make the yeast contain trace elements such as selenium and chromium, it will have certain curative effect on some diseases. If selenium-containing yeast is used to treat Keshan disease and Kaschin-Beck disease, it can prevent cell aging to some extent; Chromium-containing yeast can be used to treat diabetes.
Feed use
Feed yeast: usually cultivated and dried by Candida or Kluyveromyces fragilis, it has no fermentation power and the cells are in a state of death. It is rich in protein (about 30 ~ 40%), B vitamins, amino acids and other substances, and is widely used as a protein supplement for animal feed. It can promote the growth and development of animals, shorten the feeding cycle, increase the amount of meat and eggs, improve the meat quality and lean meat rate, improve the luster of fur and enhance the disease resistance of young animals.
Physiological characteristics of yeast
Yeast is a single-celled microorganism. It belongs to fungi of higher microorganisms. Like the cells of higher plants, it has nucleus, cell membrane, cell wall, mitochondria, the same enzymes and metabolic pathways. Yeast is harmless and easy to grow. It exists in air, soil, water and animals. You can survive with or without oxygen.
Yeast is facultative anaerobic, but no obligate anaerobic yeast was found. In the absence of oxygen, fermentation yeast obtains energy by converting sugar into carbon dioxide and ethanol (commonly known as alcohol)
Most yeasts can be isolated in an environment rich in sugar, such as some fruits (grapes, apples, peaches, etc. ) or plant secretions (such as cactus juice). Some yeasts live in insects. Yeast is a single-celled eukaryote, which is usually spherical, oval, sausage-shaped, oval, lemon-shaped or lotus-shaped, much larger than the single-celled individual of bacteria, generally 1 ~ 5 or 5 ~ 20 microns. Yeast cannot swim without flagella. Yeast has a typical eukaryotic cell structure, including cell wall, cell membrane, nucleus, cytoplasm, vacuole, mitochondria and so on. , and some have microsomes.
The genetic material composition of yeast: nuclear DNA, mitochondrial DNA and special plasmid DNA.