Carbon source is the skeleton of the cellular components of microorganisms, and is the energy source of cell metabolism. Carbon sources are mainly divided into three categories: carbohydrates, oils and fats, alcohols, hydrocarbons and organic acid salts.
1 Carbohydrate carbon source
Glucose is the most widely available source of fast-acting sugar, but it should be noted that excessive glucose can cause glucose effect, which is the substrate repression effect. This is because of excessive accumulation of pyruvic acid, lactic acid and acetic acid in the case of excessive glucose or insufficient ventilation. The decrease in pH causes the activity of the enzyme system to decrease, thereby affecting the level of microbial metabolism and product synthesis.
The two sugars of maltose, which are condensed by α-glycosidic bonds, are the most important raw materials in the beer industry.
The main component of sucrose molasses.
The lactose antibiotic industry is widely used, and there is little repression effect on the synthesis of antibiotics. The slow utilization of lactose can delay the fermentation cycle and increase the amount of product synthesis.
The products of dextrin alpha amylase degrading starch are commonly used in corn starch, wheat starch, oat starch, and sweet potato starch, corn starch for nucleotide, amino acid, enzyme preparation and antibiotic fermentation; wheat starch, oat starch for organic Fermented molasses of acid alcohols Whether it is sugar cane molasses or sugar in beet molasses, most of them are fermentable sugars. After dilution, some nutrients are added, and yeast can be fermented to produce alcohol. The use of molasses to produce alcohol can eliminate the steps of cooking, koji, saccharification, etc., with low production cost, simple equipment, short production cycle and simple process operation. However, because there are a large number of non-sugar components in the molasses, especially the presence of salts and heavy metal ions, inhibition of yeast reproduction and alcohol production, so the molasses should be treated before fermentation.
The dry matter concentration of cane molasses is generally 80-90Bx, first diluted to 30-40Bx to reduce the viscosity; sulfuric acid or phosphoric acid (about pH 4.5) to precipitate pigment and release volatile acid, the original pH of sugar cane molasses is about 5, Sometimes it is not necessary to adjust; boil and heat for about 30 minutes to remove volatile harmful components such as SO2 and formic acid.
Caramel, melanin and pectin in molasses should be removed to improve equipment utilization and fermentation rate. The molasses has many impurities and low purity, which not only causes the fermentation rate to decrease, but also causes the equipment to be easily fouled. Therefore, the ash and impurities in the molasses should be removed as much as possible. Molasses contains trace amounts of metal ions, especially copper ions, which inhibit yeast. When the copper ion content reached 5 mg/L, the yeast began to be inhibited, and when the content reached 10 mg/L, the yeast stopped growing. Therefore, a small amount of heavy metal ions in the molasses should cause sufficient attention.
As a fermentation medium, molasses also needs to add appropriate nutrients in order to coordinate the proportions of the various ingredients. There are many non-sugar impurities in molasses and many bacteria. This requires strong yeast strain, high temperature resistance, high acid resistance and high osmotic pressure.
2 fat carbon source
The oils and fats that can be used by microorganisms are mainly animal and vegetable oils. Microorganisms can use their own lipases to decompose lipids to obtain glycerin and fatty acids. Lipids need to be highly ventilated as a carbon source. Otherwise, fatty acids will accumulate and pH will drop.
Oils and fats are also good defoamers.
Commonly used oils and fats are: soybean oil, rapeseed oil, lard, cottonseed oil, corn oil, linseed oil, olive oil
3 organic acids, alcohols, hydrocarbons
Commonly used organic carbon sources include: lactic acid, acetic acid, citric acid, fumaric acid, sorbitol, ethanol, organic acids commonly used as a carbon source, such as sodium acetate is commonly used in algae fermentation medium.
Penicillin fermentation can use ethanol as a carbon source.
Sorbitol is an important intermediate for vitamin C.
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