Biomedical Engineering Reference
In-Depth Information
unit volume per unit time). This aspect is greatly favored in the production of growth-asso-
ciated products.
Fed-batch operation allows the replacement of water loss by evaporation and decrease of
the viscosity of the broth such as in the production of dextran and xanthan gum, by addition
of a water-based feed. Also, fed-batch might be the only option for fermentations dealing
with toxic or low-solubility substrates.
Comparing with chemostat operations, fed-batch operation offers a continued presence of
certain substances in the reactor. When dealing with recombinant strains, fed-batch mode can
guarantee the presence of an antibiotic throughout the course of the fermentation, with the
intent of keeping the presence of an antibiotic-marked plasmid. Since the growth can be regu-
lated by the feed, and knowing that in many cases a high growth rate can decrease the expres-
sion of encoded products in recombinant products, the possibility of having different feeds
and feed modes makes fed-batch an extremely flexible tool for control in these cases.
Because the feed can also be multisubstrate, the fermentation environment can still be
provided with required protease inhibitors that might degrade the product of interest,
metabolites, and precursors that increase the productivity of the fermentation.
Finally, in a fed-batch fermentation, no special piece of equipment is required in addition
to that one required by a chemostat, even considering the operating procedures for steriliza-
tion and the preventing of contamination.
A cyclic fed-batch culture has an additional advantage: the productive phase of a process
may be extended under controlled conditions. The controlled periodic shifts in growth rate
provide an opportunity to optimize product synthesis, particularly if the product of interest
is a secondary metabolite whose maximum production takes place during the deceleration in
growth.
Advantages:
Production of high cell densities due to extension of working time (particularly important
in the production of growth-associated products)
Controlled conditions in the provision of substrates during the fermentation, particularly
regarding the concentration of specific substrates as for example the carbon source
Control over the production of by-products or catabolite repression effects due to limited
provision of substrates solely required for product formation
The mode of operation can overcome and control deviations in the growth pattern as
found in batch fermentation
Allows the replacement of water loss by evaporation
Alternative mode of operation for fermentations leading with toxic substrates (cells can
only metabolize a certain quantity at a time) or low-solubility compounds
Increase of antibiotic-marked plasmid stability by providing the correspondent antibiotic
during the time span of the fermentation
No additional special piece of equipment is required as compared with the continuous
fermentation mode of operation
Disadvantages:
It requires previous analysis of the microorganism, its requirements, and the
understanding of its physiology with the productivity
Search WWH ::
Custom Search