Introduction to Carbon Source Substances for Microbial Cultivation

The nutrients used to form the carbon source in microbial cells and metabolites are called carbon sources. The carbon content in microbial cells accounts for about 50% of the dry matter. Carbon source is one of the main components of industrial fermentation medium, which can not only form bacterial cells and metabolites, but also provide the energy required for microbial life activities. The carbon sources used in production include carbohydrates (sugars), fats, organic acids, alcohols, and hydrocarbons. Due to the different physiological characteristics of various microorganisms, the carbon source degrading enzymes contained are not completely consistent, and the types of carbon sources used may vary.
The sugars used in industrial fermentation can be divided into monosaccharides, disaccharides, starches, and molasses. Glucose is the most commonly used monosaccharide in industrial fermentation, prepared by starch processing. Its products include solid powdered glucose and glucose syrup (containing a small amount of disaccharides). They are widely used in fermentation production of antibiotics, amino acids, organic acids, polysaccharides, and chitin conversion. Most microorganisms can use glucose as a carbon source, while xylose and other monosaccharides are rarely used in production due to cost and other reasons. Swallow sugar and lactose used in industrial fermentation are available in pure form, as well as in molasses and whey containing these two sugars. Maltose is often used in its syrup. Mainly used for fermentation of antibiotics, amino acids, organic acids, and enzymes. The molasses used in production includes sugar beet waste syrup and sugarcane waste syrup.
Corn starch and its hydrolysate are commonly used carbon sources in fermentation for antibiotics, amino acids, nucleic acids, enzyme preparations, etc. Potatoes, wheat, oat starch, etc. are used in the production of organic acids, alcohols, etc. Liquefied starch can be gradually broken down into glucose by extracellular amylase and amylase produced by microorganisms, and absorbed and utilized by bacterial cells.
According to the speed at which microorganisms utilize carbon sources, carbon sources can be classified as readily metabolized carbon sources, such as glucose and raffinose; Gradely metabolized carbon sources, such as lactose and starch. Carbohydrates such as glucose, which are easily utilized by bacterial cells, have a feedback regulatory effect on the synthesis of many products. Attention should be paid to controlling their concentration or forming a mixed carbon source with polysaccharides that are slowly utilized by bacterial cells, which is beneficial for the synthesis of target products. In penicillin fermentation, glucose can inhibit the synthesis of penicillin, while lactose has almost no inhibitory effect on the synthesis of penicillin. If low-cost glucose is used as the carbon source for penicillin synthesis, control methods such as flow addition should be employed.