Glycerol from biodiesel industry, which is available in high amounts
nowadays, is a renewable low-cost substrate that can be used for
many biotechnological applications. Yarrowia lipolytica is a strictly
aerobic yeast, known for the ability to use several carbon sources
and to produce several high value compounds. Citric acid, an intermediate
of tricarboxylic acids cycle, is extensively used in food
and pharmaceutical industry. This organic acid can be produced
by Y. lipolytica from glycerol under specific growth conditions,
namely under nitrogen limitation. Oxygen availability in the culture
medium is also an important factor that influences these aerobic
bioprocesses.
In this work, the influence of Oxygen Transfer Rate (OTR) from
air to the culture on citric acid production by Y. lipolytica W29
(ATCC 20460:CLIB89) using crude glycerol was evaluated. Batch
cultures with 50 g L1 of glycerol were performed at OTR values
from 52mgL1 h1 to 878mgL1 h1 obtained varying aeration
and agitation rates, from 1vvm to 3 vvm, and from 200rpm to
600 rpm, respectively.
The increase of OTR up to 408mgL1 h1 leaded to a 7.7-fold
increase of citric acid production (10.8±0.5gL1). Further increase
of OTR values above 408mgL1 h1 did not improve citric acid concentration
and productivity. In fact, for these OTR values oxygen
dissolved concentration in the medium was kept above 50% of the
saturation value, during the production of citric acid, meaning that
the process control by oxygen limitation was prevented
