Introduction
- Fermentation is the technique of biological
conversion of complex substrates into simple compounds by various
microorganisms such as bacteria and fungi.
- In the course of this metabolic breakdown, they
also release several additional compounds apart from the usual products of
fermentation, such as carbon dioxide and alcohol. These additional
compounds are called secondary metabolites.
- Secondary metabolites range from several
antibiotics to peptides, enzymes and growth factors.
- The development of techniques such as Solid State
Fermentation (SSF) and Submerged Fermentation (SmF) has lead to
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)/Liquid Fermentation
(LF) SmF utilizes free-flowing liquid substrates, such as molasses and
broths.
- The process is used for a variety of purposes,
mostly in industrial manufacturing.
Principle of Submerged Fermentation
Submerged
fermentation involves the growth of the microorganism as a suspension in a
liquid medium in which various nutrients are either dissolved or suspended as
particulate solids in many commercial media.
- Submerged fermentation is a process involving the
development of microorganisms in a liquid broth.
- This liquid broth contains nutrients and it results
in the production of industrial enzymes, antibiotics or other products.
- The process involves taking a specific
microorganism such as fungi and placing it in a small closed flask
containing the rich nutrient broth.
- A high volume of oxygen is also required for the
process. The production of enzymes then occurs when the microorganisms
interact with the nutrients on the broth resulting in them being broken
down.
- 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; they are batch-fed
fermentation and continuous fermentation.
- In batch-fed fermentation sterilized
growth nutrients are added to the culture. It 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 it is typically
highly concentrated to stop dilution. The rate of growth in the culture is
maintained by adding nutrients, this also reduces the risk of overflow
metabolism.
- An open system is constructed for continuous
fermentation. Then sterilized liquid nutrients are slowly and
continuously added to the bioreactor at the same rate at which the
converted nutrient solution is being recovered from the system. This
results in a steady-rate production of the fermentation broth.
In order to
maintain a successful fermentation, certain variables must be monitored, for
example, temperature, pH, as well as oxygen and carbon dioxide levels.
Submerged Fermentation Substrate
Some common
substrates used in submerged fermentation are 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 has the
advantages of short period, low cost and high yield.
- Purification of products is easier.
- In liquid culture the control of the
fermentation is simpler and consequently significant reductions in
fermentation times can be achieved.
- In the same way, the use of submerged culture can
benefit the production of many secondary metabolites and decrease
production costs by reducing the labour involved in solid-state
methods.
Limitations of Submerged Fermentation
- In recent years, many researchers have demonstrated
that SSF has a large impact on productivity, leading to higher yields and
improved product characteristics compared to SmF
- Low volumetric productivity
- Relatively lower concentration of the products
- More effluent generation
- Complex fermentation equipments
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