1. Extraction method: Citric acid can be directly extracted from fruits which contain citric acid. Due to the low content of citric acid in the raw material of fruits, the production efficiency of citric acid is too low and the cost is too high. The above reason leads to the result that extraction method had been eliminated.
2. Chemical synthesis method: Because the synthetic product contains plenty of isocitric acid, and it is too difficult to be solved, this chemical synthesis method had also been eliminated.
3. Fermentation method:
① Solid fermentation: For example, the bagasse and beet slag are used as solid raw materials for culture fermentation. The solid fermentation method requires a large number of labor intensity, the production efficiency of citric acid is relatively low, so the solid fermentation method is not suitable for large-scale industrial production, and the solid fermentation method had been eliminated;
② Liquid deep fermentation: Liquid deep fermentation uses the large-scale fermenter, the production scale is large, the production efficiency of citric acid is high , the cost is low, therefore liquid deep fermentation has become the first choice for current citric acid production;
1. Source of citric acid fermentation raw materials: The crops which contain starch , finished industrial products and industrial waste can be used as the raw materials for fermentation production of citric acid.
ü Crops: corn, rice, wheat, cassava, sweet potato, potato, etc.;
ü Finished industrial products: starch, glucose, etc.;
ü Industrial waste: glucose mother liquor, beet waste, bagasse waste, etc.;
2. Principle of selecting raw materials:
ü Availability: plenty of quantity, easy to obtain, cheap, easy to store;
ü Processability: good quality, high starch content, simple processing technology;
ü Safety: For products which are required to use non-GMO raw materials, it is necessary to avoid the selection of GMO suspected raw materials, such as corn;
1. Mixed materials with residue fermentation:
For example: dried sweet potato at early stage and dried cassava are used to conduct the residue fermentation for obtaining citric acid.
① Advantages: Only simple pretreatment of the raw materials are required.Crushing, pulping and liquefaction(direct liquefaction in single tank) are required;
② Disadvantages:More residue, high stirring power, low mass transfer efficiency;Effective glucose concentration is low;Concentration of target product is low ; Extraction yield rate is low; The amount of mycelium residue is large, which contains a lot of residues from raw materials, and the utilization value is low;
2. Clear liquid fermentation after removing residue:
For example: Corn and cassava are used to clear liquid fermentation after removing residue. This fermentation method adopts dry processing technology. The raw material is crushed, liquefied and filtered to obtain the liquid glucose , and then some unfiltered corn liquid is added to form the fermentation culture medium of citric acid.
① Advantages: After removing residues, the culture conditions are effectively improved, and the mass transfer efficiency is improved under the same stirring conditions; Effective glucose concentration is high; Concentration of target product is high; Extraction yield rate is is high, and it prefers to lose glucose, but it chooses to lose less citric acid. Comprehensive utilization of glucose and residue, so as to offset the cost;
② Disadvantages: Raw material pretreatment process is complex, but automatic control makes it feasible; Part of the unfiltered corn liquid is added, there is still plenty of mycelium residue, which still contains plenty of residue from raw materials,so the value of use is not high;Raw materials have not been fully processed, the added value of glucose residue is low;
3. Complete formula clear liquid fermentation:
The glucose syrup and glucose mother liquor by deep processing of using of corn, wheat and other materials as the main raw materials, and then a variety of nutrients are supplemented, then citric acid fermentation culture medium is worked out.
① Advantages: Formula culture medium and whole clear liquid fermentation have further improved the culture conditions, so mass transfer efficiency is further improved under the same stirring conditions; The effective glucose concentration is further improved;The concentration of target product is further increased; The mycelium amount is small, the purity is high,so the comprehensive utilization value is high, such as the extraction of chitin; The raw materials have been fully processed, which effectively realizes the increase of the added value of raw materials as far as possible;
② Disadvantages: The source of raw materials is limited, and the storage of raw materials is not convenient enough; The corresponding raw material is required to support deep processing plant, such as wet corn processing plant, wet wheat processing plant,etc.;