Penicillin Production - DCU

vital component of aerobic metabolism, it is essential that there is good transfer of
oxygen across the gas/liquid interface. The Sparger delivers this oxygen. One problem
with gas/liquid interfaces is the formation of foam. The impeller that serves to break
up the foam generally relieves this.
Heat Transfer is important because metabolism as a process tends to give off heat, as
does the mechanical mixing by the impellers. If the reactor needs to be operated at a
constant temperature of range of temperatures, then it is critical that there is some
kind of system to cool the reactor. This is normally achieved through a combination
of a cooling jacket and cool water being passed around the tank.
Bulk Flow and Mixing are achieved by the impellers. Most reactors use the Rushton
Flat-bladed disc turbine seen in the diagram. Fluid flow in a reactor can be described
as Newtonian or non-Newtonian. Newtonian fluids show constant viscosity and linear
shear rate against shear stress. However many fluids are non-Newtonian and are
described as Bingham or Pseudoplastic.
Batch, Fed-Batch and Continuous Culture are terms used to describe how nutrients
and substrate will be delivered to a culture in a reactor. Batch simply means that a
fixed amount of substrate is added at the beginning of the process. Fed Batch means
that substrate is added in small increments at various times in the fermentation.
Continuous means that substrate is constantly added to the reactor while an equal
amount of fermented medium is removed.
Steam is used to keep the reactor running aseptically. This is achieved because the
reactor is designed as a pressure vessel and steam is sent through at a minimum
temperature/pressure of 121 0 C/15 psi for 15-30min.
So much for our discussion of basic reactor design. What follows is a brief description
of the specific fermentation conditions necessary for the production of penicillin.
Special fermenter Conditions for the production of Penicillin
Aside from what is described above, there are a few specific characteristics of
penicillin that must be considered when attempting fermentation:
• Most penicillins form filamentous broths that are pseudoplastic (non-
Newtonian) in nature. This means they can be difficult to mix due to their high
(and not constant) viscosity. Also the increasing viscosity of the broth can
hinder oxygen transfer. Which leads to the next point.
• Penicillin is an aerobic organism; therefore the rate of oxygen supply is critical
to the fermentation. Thus, the reactor must have an efficient oxygen supply
system.
7