l-Glutamic acid production was investigated in 3.5 dm3
laboratory scale bioreactors in order to find out the oxygen
transfer strategy, maximising the product and minimising
the by-products, which is an important operational parameter
of the bioreactor, that is clear in the metabolic pathway of
the GA producing micro-organisms. The effects of agitation
rate and air flow rate on GA, other amino acids, and organic
acids, were investigated and the oxygen transfer conditions
maximising the GA yield and selectivity were found.
Higher or lower than the optimum decreased the yield and
selectivity significantly. The transient oxygen transfer condition
LimO applied in this work was detrimental for GA
production. On the other hand, MO2, where step increase
to agitation rate was applied, resulted almost equivalent GA
concentration and selectivity as LO1. Therefore, sufficient
oxygen transfer was actually essential in the growth phase
of the cells, and it does bring a marked change in glutamic
acid formation, on the contrary to the results obtained with
Brevibacterium lactofermantum [11], it was found that
medium oxygen transfer, which can be maintained with
appropriate oxygen/air and agitation rates depending on
the configuration and scale of the bioreactor used is necessary
for maximum GA production and selectivity. The
by-product distributions obtained at different extents of
oxygen transfer are in accordance with the necessitates of
the metabolic pathways of the cells. Lower oxygen transfer
conditions increased pyruvic and/or lactic acid concentration;
while higher oxygen transfer conditions obtained by
increasing the agitation rate increased -ketoglutaric acid
and succinic acid concentrations. The results of this work is
being used for the calculations of metabolic fluxes for the
effect of oxygen transfer to maximised GA