Biomedical Engineering Reference
In-Depth Information
It requires a substantial amount of operator skill for the setup, definition, and
development of the process
In a cyclic fed-batch culture, care should be taken in the design of the process to ensure that
toxins do not accumulate to inhibitory levels and that nutrients other than those
incorporated into the feed medium become limiting. Also, if many cycles are run, the
accumulation of non-producing or low-producing variants may result
The quantities of the components to control must be above the detection limits of the
available measuring equipment.
13.5. CONSIDERATIONS IN IMPLEMENTING FED-BATCH
OPERATIONS
Fed-batch operations can be implemented to mimic CSTR operations or to control culture
variations. Before considering fed-batch operations, one should learn from a batch
fermentation:
Optimum abiotic conditions such as temperature, light, agitation, pH, growthmedium, etc.
Specific needs of precursors, inducers or other enrichment factors
The different growth phases and the consumed (substrate) and produced components
(product of interest and by-product)
The relationship between the biomass and product formation (growth- or non-growth-
associated product) and the oxygen uptake rates
Limiting substrate for growth and the relationship between the specific growth rate and
the limiting substrate concentration
Eventual inhibitions from the substrate and/or product. Fed-batch is ideal for substrate-
inhibited systems, whereas not proper for product-inhibited systems.
Fed-batch operation is ideal for high production rate needs, yet unsuitable for continuous
cultivation, for example, due to microorganism instability. For example, cultivation of genet-
ically engineered organism is commonly conducted with fed-batch operations to increase
productivity.
13.
6. EXAMPLES OF FED-BATCH USE IN INDUST
RY
The use of fed-batch culture by the fermentation industry takes advantage of the fact that
the concentration of the limiting substrate may be maintained at a very low level, similar to
a CSTR or a chemostat; thus,
Avoiding repressive effects of high substrate concentration
Controlling the organism's growth rate and consequently controlling the oxygen demand
of the fermentation.
Saccharomyces cerevisiae
is industrially produced using the fed-batch technique so as to
maintain the glucose at very low concentrations, maximizing the biomass yield and mini-
mizing the production of ethanol (due to Crabtree effect), the chief by-product.
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