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
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 PenicilliumandAspergillus.
–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.
The science of fermentation is known as zymology. Microorganisms play an important role in the fermentation technology. Through their actions the fermentation process transforms and preserves food. Thousands of years ago, people have started fermenting food. Now we have other techniques to preserve food still the fermentation process persists. People are interested in fermented food due to its interesting flavours, their vitamins and enzymes, or organic acids and “good bacteria”.
BACKGROUND OF FERMENTATION TECHNOLOGY:
Fermentation comes under the umbrella of industrial microbiology (it’ the interdisciplinary study that uses microbes, to produce commercial products or carry out important chemical transformations usually grown on large scale). So fermentation can be carried out both in small scale and large scale production.
Now the microbial biotechnology joined with the industrial microbiology which leads to many fold increase of products and also to produce New products, by means of genetic manipulations of these microorganisms which are originally not produced by these microorganisms.
Fermentation refers to any large scale process in which the commercial products like vitamins, enzymes, vaccines, organic acids are produced from the raw materials by using different microorganisms either aerobically or anaerobically.
In microorganisms, fermentation is the aerobic degradation of organic nutrients to produce adenosine triphosphate (ATP) for their growth.
The product that is produced during fermentation(or microbial growth) was of two groups.
Primary metabolites :It’s the product which is formed during the active growth stage (log phase) of the microorganism.
Ex. Alcohol produced by yeast. By the action of primary metabolic pathway of yeast (EMP pathway), the alcohol is produced and will be accumulated during the active growth stage of yeast.
Secondary metabolites :These are the products which are formed either at the end of active growth stage or at the beginning of the stationary phase are referred to as secondary metabolites.
Example: Antibiotics are usually produced in the stationary phase. These are formed by the secondary metabolic pathways That is not essential for the growth of microorganisms. Few organisms show this characteristic.
TYPES OF FERMENTATION :
There are various types of fermentation process based on its characteristics.
Based on the state, the fermentation process can be classified into two.
Submerged (liquid) fermentation :Fermentation is carried out in liquid forms.
Ex. From sugarcane industrial waste alcohol can be produced- Molasses by yeast.
Solid fermentation :With about 30-50% moisture level the Fermentation is carried out in solid condition.
Example: Gibberellic acid produced from grains by fungus Fusarium moniliformi
Based on the microbial growth (culturing method):
Batch fermentation :It is a closed system of microbial fermentation in which the volume is already fixed.
Fed batch fermentation :As the fermentation process is continuing the substrate for fermentation (raw material) is added in increments.
Continuous fermentation :It is an opened system of microbial fermentation in which the input (nutrients solutions or media) is added continuously with the withdrawal of equal portion of converted or fermented solution.
LARGE -SCALE FERMENTATIONS:
Fermentation process is carried out in a closed vessel which is called as Fermentor. The volume of the Fermentor may varies from 5-10 lit to 500,000 lit. Similarly the Fermentor model will vary for both aerobic and anaerobic process.
DESIGN AND PARTS OF FERMENTOR :
There are various types of Fermentor. But the basic structure of Fermentor is as follows:
The components are:
Inlet :to add the the substrates for microorganisms etc
Outlet :to collect the products and check the samples
Stirrer :to mix the contents inside the Fermentor
Air sparger :by releasing small bubbles into the Fermentor to provide oxygen to the microorganisms
pH meter : to check the pH and maintaining by adding acid or alkali
Thermometer : to check the temperature
Outer jacket :for cooling process ( because during the Fermentation, lot of heat will be generated)
Sterilization unit :stem is supplied to sterilize the medium and container
Scale up : it refers to sequence wise step in any Fermentation to yield Maximum product
Scale up of fermentation
INDUSTRIAL APPLICATION OF FERMENTATION PROCESS :
Presently, “ Fermentation technology” is replaced by the word “Bioprocess technology” . The commercial products formed by the fermentation technology is very useful for the industrial purposes.
The following are the commercial products obtained through the fermentation process by different microorganisms.
Most of the antibiotics can be produced by microbial fermentations. Sometimes, the antibiotic needs to be modified through some chemical processes, referred as semi- synthetic antibiotics. Here are some antibiotics and the organisms involved in its production.
Vitamin B12 and Riboflavin are vitamins which is commercially produced by pseudomonas denitrificans and Ashbya gossipii respectively.
L-glutamate, L- aspartate, glycine, cysteine, tryptophan etc are some common amino acids commercially produced by microbes.
Presently, these amino Acids can be produced by genetically modified bacteria.
For conversion of one compound to another product the microorganisms act as bio-catalyst in bio conversion process.
Ex. Most of the steroids are produced by this process
Enzymes can also be produced by fermentation process which is mostly used in food industry and molecular biology.
The following table shows the enzymes and the involved organisms
Bacillus licheniformis, Aspergillus
Acetic acid, citric acid, acetone, butanol etc are produced by microorganisms.
Single cell protein
By using fermentation technology protein is also produced which can be used as food referred to as Single cell proteins (SCP)
Example: The yeast, chlorella, spirulina etc .
Alcohols and alcoholic beverages
The yeast play a major role in the alcohol industry. As we know it is a facultative aerobe it can be grown aerobically and anaerobically. When, yeast grows aerobically its biomass increased with low alcohol, used for the production of baker yeast while if it grows anaerobically, the alcohol production will be Maximum.
Example: Whiskey, rum, otka etc are the commercial preparations of alcohol.
The microorganisms itself can be used as food. Following are some of the foods obtained from microbes.