Submerged fermentation is a type of fermentation in which the microorganisms are suspended in a liquid medium. The liquid medium also contains various other nutrients and growth factors in the necessary proportions in a dissolved or a particulate solids form.
The main application of submerged fermentation technique is in the extraction of metabolites (secondary metabolites) which are needed to be in liquid form for use.
APPLICATIONS OF SUBMERGED FERMENTATION
- The primary application of submerged fermentation is in the extraction process of metabolites (mostly secondary metabolites) that find applications in their liquid form.
- Citric acid is one of the most important metabolites as the production volume of it is high, for the production of antibiotics like penicillin.
- Submerged liquid fermentations are traditionally used for the production of microbially derived enzymes like cellulolytic enzymes.
CITRIC ACID PRODUCTION
- Citric acid is widely distributed in plant and animal tissues.
- It is an intermediate of the Krebb’s cycle, by which carbohydrate gets converted to CO2, in nature.
- Citric acid can be produced on the industrial scale by employing submerged state fermentation as the fermentation method.
Type of bioreactor used for submerged fermentation:
- Stirred tank bioreactor
- Airlift fermenter.
Selection of strain and storage:
- Various criteria should be checked for the selection of production strains such as:
-High citric acid yield.
-Stability of the strain.
-Adequate amount of sporulation, etc.
Microorganisms used for the production of citric acid:
-Species of Penicillium and Aspergillus.
–Aspergillus niger is used as the principal fungus for citric acid production as it can produce large quantities of citric acid while growing on a carbohydrate medium.
- Maintenance of the culture of the selected strain is the next important step in citric acid production and is done so by the storage of spores.
Steps used to carry out fermentation to ensure abundant production:
-High sugar concentration.
-Limited nitrogen/phosphorus concentration.
-Very low concentration of heavy metals like iron and manganese.
Submerged fermentation process:
-The strain used for the submerged fermentation of citric acid is Aspergillus japonicus.
-The organism shows sub-surface growth.
-Citric acid is produced within the culture solution.
-Using submerged fermentation for the production of citric acid is economical as compared to other fermentation methods.
Uses of citric acid:
- It Is extensively used in the production of carbonated drinks.
- It is used in plasticizers.
- It is used as a chelating and sequestering agent.
- Used in the pharmaceutical and food industries as an acidulant.
The advantages of submerged fermentation include:
- The duration of the process is short, therefore saves time.
- The overall cost of the process is low and the yield of products is high, making it a very economical process.
- The process of purification and processing of the products is far simpler compared to other processes.
- The cost of handling is low and the handling of the fermenter is easy therefore it reduces the labour involved.
- The overall volumetric productivity of this process is low.
- The effluent that is generated during the process is high in quantity.
- The equipment that is used is expensive and complex.
- The products that are obtained by using this process may be of low concentration.
Article by– Shaily Sharma (MSIWM041)