Fermentation is the technique of biological conversion of complex substrates into simple compounds by various microorganisms such as bacteria and fungi.
During this metabolic breakdown, microorganisms release several additional compounds besides the usual products of fermentation, such as carbon dioxide and alcohol.
These additional compounds are known as secondary metabolites.
Secondary metabolites include a wide range of substances such as antibiotics, peptides, enzymes, and growth factors.
The development of techniques like Solid State Fermentation (SSF) and Submerged Fermentation (SmF) has enabled industrial-level production of bioactive compounds.
Submerged fermentation
Submerged fermentation is a method of manufacturing biomolecules in which enzymes and other reactive compounds are submerged in a liquid such as alcohol, oil, or a nutrient broth.
Submerged Fermentation (SmF), also known as Liquid Fermentation (LF), utilizes free-flowing liquid substrates, such as molasses and broths.
This process is used for a variety of purposes, mostly in industrial manufacturing.
Principle of Submerged Fermentation
Submerged fermentation involves the growth of microorganisms as a suspension in a liquid medium, where various nutrients are either dissolved or suspended as particulate solids in many commercial media.
It is a process that develops microorganisms in a liquid broth.
This liquid broth contains nutrients and leads to the production of industrial enzymes, antibiotics, or other products.
The process includes placing a specific microorganism, such as fungi, into a small closed flask containing the rich nutrient broth.
A high volume of oxygen is also required for the process.
Enzyme production occurs when microorganisms interact with the nutrients in the broth, leading to their breakdown.
The bioactive compounds are secreted into the fermentation broth.
Methods of Carrying Out Submerged Fermentation
There are two common methods by which submerged fermentation takes place: batch-fed fermentation and continuous fermentation.
In batch-fed fermentation, sterilized growth nutrients are added to the culture.
This method is most common in bio-industries as it occurs during the growth of biomass in the fermenter.
It helps raise the cell density in the bioreactor and is typically highly concentrated to prevent dilution.
The rate of growth in the culture is maintained by adding nutrients, which also reduces the risk of overflow metabolism.
In continuous fermentation, an open system is constructed where sterilized liquid nutrients are slowly and continuously added to the bioreactor at the same rate as the converted nutrient solution is recovered from the system.
This results in a steady-rate production of the fermentation broth.
To maintain successful fermentation, certain variables must be monitored, such as temperature, pH, and oxygen and carbon dioxide levels.
Submerged Fermentation Substrate
Some common substrates used in submerged fermentation include soluble sugars, molasses, liquid media, fruit and vegetable juices, and sewage/wastewater.
Applications of Submerged Fermentation
SmF is primarily used in the extraction of secondary metabolites that need to be used in liquid form.
Submerged liquid fermentations are traditionally used for the production of microbially derived enzymes.
Advantages of Submerged Fermentation
Submerged fermentation technology offers advantages such as a short production period, low cost, and high yield.
Purification of products is easier.
In liquid culture, controlling the fermentation process is simpler, leading to significant reductions in fermentation time.
The use of submerged culture benefits the production of many secondary metabolites and decreases production costs by reducing the labor required in solid-state methods.
Limitations of Submerged Fermentation
Recent studies have shown that Solid State Fermentation (SSF) often results in higher yields and improved product characteristics compared to Submerged Fermentation (SmF).
SmF has low volumetric productivity.
It typically produces relatively lower concentrations of the desired products.
It generates a larger volume of effluents.
The process requires complex fermentation equipment.
References
ScienceDirect. Topics in Agricultural and Biological Sciences: Submerged Fermentation. Available at: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/submerged-fermentation
UK Essays. A Comparative Study on Submerged and Solid State Fermentation. Available at: https://www.ukessays.com/essays/biology/submerged-and-solid-state-fermentation-biology-essay.php
ResearchGate. Platform for Scientific Publications and Research Sharing. Visit: https://www.researchgate.net/
David Moore's World of Fungi. 21st Century Guidebook to Fungi - Chapter 17.12: Fermentation Technology. Access at: http://www.davidmoore.org.uk/21st_Century_Guidebook_to_Fungi_PLATINUM/Ch17_12.htm
SlideShare. Fermentation Technology Presentation by Deepak Bajantri. Available at: https://www.slideshare.net/DeepakBajantri/fermentation-technology-59569219
OMICS Online. Scholarly Articles, Journals, and Presentations on Submerged Fermentation. Explore: https://www.omicsonline.org/scholarly/submerged-fermentation–journals-articles-ppts-list.php
AGRIS – FAO. Submerged Fermentation Records and Research Summaries. Search: http://agris.fao.org/agris-search/search.do?recordID=CN2006001496
SpringerLink. Research Article: Submerged Fermentation Approaches and Developments. View at: https://link.springer.com/article/10.1023/A:1023609427750
EuropePMC. Scientific Abstract on Submerged Fermentation Methods. Access: http://europepmc.org/abstract/cba/602507
ScienceDirect. Topics in Nursing and Health Professions: Submerged Fermentation. Read more: https://www.sciencedirect.com/topics/nursing-and-health-professions/submerged-fermentation
Answers.com. Common Disadvantages of Submerged Fermentation. Read at: http://www.answers.com/Q/What_are_the_disadvantages_of_submerged_fermentation
Science.gov. Liquid-State Fermentation Topics and Research. Browse: https://www.science.gov/topicpages/l/liquid+state+fermentation
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