The word “fermentation” originates from the Latin word Fervere which means to boil. The boiling appearance is due to the appearance of bubbles on fruit/malted grain extracts which indicates the CO2 production.
Fermentation is a
process for the production of a product by the mass-culture of a microorganism
under optimized conditions.
Based on the products formed, there are different types of Fermentation
which are:
o Production of Microbial cells/biomass
o Production of Microbial enzymes
o Production of Microbial metabolites
o Production of Recombinant products
o Production of Modified compound than which is
added at the beginning- Transformation
Major Steps in Fermentation
- Media
formulation- for inoculum development and for
production fermenter
- Sterilization
of medium, fermenters, ancillary
equipments
- Production of an
active, pure culture in sufficient quantity to inoculate production
vessel (Inoculum development)
- Growth of the
organism in the production fermenter under optimum conditions for product
formation (Fermentation)
- Extraction of the
product and its processing (Downstream processing- DSP)
- Disposal of
effluents produced in the process
Media Formulation
Fermentation media must satisfy all the nutritional requirements of the
microorganism and promote the synthesis
of the target product, which is either the cell biomass or a specific metabolite.
Most fermentations require liquid media/ broth (Submerged
Fermentation-SmF/surface fermentation), although some fermentations employ
solid substrates (solid state fermentation-SSF).
In an industrial fermentation process, media
are required in inoculum (starter
culture) build up and the main production
fermentation. The media formulation is different for inoculum propagation
and the actual fermentation process since they have different objectives. Inoculum
media should allow rapid/uniform growth of the inoculum whereas the production
medium should facilitate the production of desired product in good amounts. Also,
if biomass or primary metabolites
are the target product, the production medium should allow optimal growth of
the microorganism. For secondary metabolite
production, such as antibiotics, their biosynthesis is not growth related. Hence,
the media should be designed to provide an initial period of cell growth,
followed by starvation conditions. Here, the supply of one or more nutrients
(carbon, phosphorus or nitrogen source) may be limited and rapid growth does
not occur. This induces secondary metabolite production.
The media components usually are,
■ Water
■ Carbon source
■ Nitrogen source
■ Oxygen
■ Sources of P, S, minor and trace elements
■ Vitamins – Biotin, riboflavin etc
■ Buffers
■ Antifoam
■ Precursor
■ Inducer
■ Inhibitor
Most fermentations, except those involving
solid substrates, require large quantities of water in which the medium is
formulated. General media requirements include a carbon source, which provides
both energy and carbon units for biosynthesis, and sources of nitrogen,
phosphorus and sulphur. Other minor and trace elements must also be supplied,
and some microorganisms require added vitamins, such as biotin and riboflavin.
Aerobic fermentations require oxygen, and even some anaerobic fermentations require
initial aeration of media, e.g. beer fermentations. As the fermentation
proceeds different metabolic products are formed which may change the pH of the
media and it can interfere with the growth or product formation, So, to adjust
the pH, media should contain buffers or the pH is controlled by addition of acid/
alkali. Antifoam agents are also required to control foam production. Some
processes require compounds like precursor, inducer or inhibitor which are
added certain stages of the fermentation.
The composition of a fermentation medium may
be simple to complex, depending on the particular microorganism and its
fermentation. Autotrophic microorganisms require only the simplest of inorganic
media (inorganic salts, water, nitrogen source, carbon source is fulfilled by
CO2 or by carbonates) and are capable of synthesizing all the
complex organic compounds required to sustain life. Fastidious
microorganisms on the other hand lack the ability to synthesize many of their
sustenance and growth requirements. They
require the presence of many simple to complex preformed nutrients in the
medium and must have an organic carbon supply to provide for synthesis of cell
substances and release of metabolic energy.
Simple and complex media are further
subdivided into two categories: synthetic
and crude. In a synthetic medium,
all the components are specifically defined and known compounds. Each component is relatively pure and the
exact concentrations are known. Synthetic
medium has defined components and concentrations and are expensive due to the relatively
pure ingredients used. The concentration of one or several can be varied in
order to determine the effect on cell growth and product yield. Individual
components may be added or deleted as well. This has advantages in certain
types of studies. However, yields derived from these media are relatively low. Crude media contain crude factors or ill-defined
sources of nutrients and growth. They usually
allow much higher yields.
The media adopted also depend on the scale of the fermentation. For
small-scale laboratory fermentations pure chemicals are often used in
well-defined media. However, this is not always possible due to cost, as media
components may account for up to 60-80% of process expenditure.
Industrial-scale fermentations primarily use cost-effective complex crude
substrates, where many carbon and nitrogen sources are almost indefinable. Most are derived from natural plant and
animal materials, often by-products of other industries, with varied and
variable composition. The effects of
such batch-to-batch variations must be determined. Small scale trials are usually performed with
each new batch of substrate, to examine the impact on product yield and product
recovery.
The
main factors that affect the final choice of individual raw materials are as
follows:
1 Cost and availability:
ideally, materials should be inexpensive and of consistent quality and year
round availability.
2 Ease of handling in solid
or liquid forms, along with associated transport and storage costs, e.g.,
requirements for temperature control.
3 Sterilization requirements
and any potential denaturation problems.
4 Formulation, mixing, complexing
and viscosity characteristics that may influence agitation, aeration and
foaming during fermentation and downstream processing stages.
5 The concentration of target
product to be attained, its rate of formation and yield per gram of
substrate utilized.
6 The levels and range of
impurities and the potential for generating further undesired products
during the process.
7 Overall health and safety
implications.
References
- Industrial Microbiology:
An Introduction. Michael J. Waites, Neil L.
Morgan, John S
- Principles of
Fermentation Technology- Peter Stanbury, Allan Whitaker, Stephen Hall
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