Aerobic submerged fermentation

Gellan Gum. GeUan gum is the generic name for the extraceUular polysaccharide produced by the bacterium. Pseudomonas elodea (ATCC 31461). Proprietary to Kelco Division of Merck Co., Inc., geUan gum is manufactured in an aerobic, submerged fermentation (76). 

The commercial method for producing this compound involves aerobic submerged fermentation. 

Fig. 10.2 Appearance of the two major methods of vinegar production. (A) Surface fermentation is generally carried out in a tub or pot. The volume of the tab is about 4 Kl. (B, C) Because the surface fermentation proceeds slowly, it takes 1 week or longer to produce vinegar with a film forming on the liquid surface. (D) Aerobic submerged fermentation is carried out in a stainless steel tank, which volume is usually from 20 to 100 Kl. (E) Sparger air is supplied from the bottom of the tank with stirring blades. One batch of the aerobic fermentation is completed in about 2 days...

Generally, the fermentation process involves the addition of a specific culture of microorganisms to a sterilized liquid substrate or broth in a tank (submerged fermentation), addition of air if aerobic, in a well-designed gas-liquid contactor. The fermentation process is then carried out to grow microorganisms and to produce the required chemicals. Table 11-1 lists examples of the processes used by fermentation. 

Submerged fermentations are mostly operated in batch processes but can also be run continuously in certain cases (continuous fermentation). Batch fermentations may last up to 10 days. Following the fermentation the flavour raw material is extracted from the fermentation broth. In industrial fermentations typically cell counts of 10-30 g/1 are obtained. For a profitable cost/efficiency relation a product yield of 20-30 g/1 has to be achieved. Aerobe fermentations require oxygen transfer rates to the fermentation broth of about 100 mmol/1 per hour. Depending on the viscosity of the media 0.75-2.5 KW stirring power has to be applied for each m of fermentation broth. 

Citric acid fermentation is an aerobic process an increase in the oxygen supply results in an increase in citric acid yields during submerged fermentation. An interruption in the aeration, even briefly, during fermentation has been known... 

Chemical engineers are still faced with problems regarding scale-up and microbial contamination in the fermentation by aerobic submerged cultures. Despite many advances in biochemical engineering to address these problems, the problems nevertheless persist. Recently, many advances have been made in the area of recombinant DNA, which themselves have spun off new and lucrative fields in the production of plant and animal pharmaceuticals. A careful study of this technology is therefore necessary, not only for the implementation of efficient fermentation processes, but also for compliance with official regulatory bodies. 

Most industrial enzymes are produced by micro-organisms via submerged fermentation. Most fermentations are aerobic. The production process of industrial enzymes can be divided into three steps fermentation, recovery, and formulation. 

In a multistage reaction penicillin G is nowadays produced exclusively by the aerobic submerged process, whereby oxygen is introduced by aerating the base of the reactor (fermenter) strains of the mold Penicillium chrysogenum are the predominantly used microorganism. 

MacroHdes are obtained by controUed submerged aerobic fermentations of soil microorganisms. Although species of Streptomjces have dominated, species of Saccharopoljspora Micromonospora and Streptoverticillium are also weU represented. New techniques such as enzyme-linked immunosorbent assay (ELISA) based assays may prove beneficial for discovering new stmctures (464). 

The process for producing amphomycin comprises cultivating a strain of Streptomyces canus in an aqueous, nutrient-containing carbohydrate solution under submerged aerobic conditions untii substantiai antibacterial activity is Imparted to the solution and then recovering the so-produced amphomycin from the fermentation broth. 

Chloramphenicol may be prepared by fermentation or by chemical synthesis. The fermentation route to chloramphenicol is described in U.S. Patents 2,4B3,B71 and 2,4B3,B92. To quote from U.S. Patent 2,4B3,B92 The cultivation of Streptomyces venezuelae may be carried out in a number of different ways. For example, the microorganism may be cultivated under aerobic conditions on the surface of the medium, or it may be cultivated beneath the surface of the medium, i.e., in the submerged condition, if oxygen is simultaneously supplied. 

Different routes for converting biomass into chemicals are possible. Fermentation of starches or sugars yields ethanol, which can be converted into ethylene. Other chemicals that can be produced from ethanol are acetaldehyde and butadiene. Other fermentation routes yield acetone/butanol (e.g., in South Africa). Submerged aerobic fermentation leads to citric acid, gluconic acid and special polysaccharides, giving access to new biopolymers such as polyester from poly-lactic acid, or polyester with a bio-based polyol and fossil acid, e.g., biopolymers . 

The original mold observed and preserved by Alexander Fleming was a strain of Penicillium notatum, a common laboratory contaminant. Later, cultures of Penicillium chrysogenum were found to be better producers of penicillin, and the present industrial strains have been derived from this species. The original strains produced the antibiotic only by surface fermentation methods and in very low yields. Improved media and productive strains under submerged aerobic fermentation conditions led to dramatic yield increases. Subsequent improvements, principally in culture selection and mutation, further improved yields, reaching 20-30 g/L. 

Derivation By submerged aerobic fermentation, filtration, solvent extraction, and crystallization. 

Derivation From sorbitol by submerged culture aerobic fermentation. 

The most common procedure for large-scale aerobic fermentations is to use deep tanks of a stirred liquid medium. Efficient air exchange is obtained by continuous pumping of sterile air into crossed or coiled perforated pipe placed at the bottom of the tank at rates of up to one volume of air per unit of medium volume per minute [62]. This method promotes aerobic growth throughout the medium, which accomplishes large volume production in a limited space. But it also has problems, which relate to the maintenance of sterility and occasionally from foam formation. Overall, however, submerged... 

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