Nowadays, there is a great interest in the development of technologies for
ethanol production as an alternative combustible, since it can be used instead
of petrol or to blend with petrol, reducing the country’s dependence on oil
and imported fuel. It is known that the ethanol production by fermentation
is influenced by several process conditions such as pH, temperature, medium
composition, oxygen availability, among others. Determining the most suitable
fermentation conditions is of large importance for the establishment of a
successful technology. In the present work, the influence of oxygen transfer
volumetric rate (KL
a) on xylose to ethanol bioconversion by the yeast Pichia
stipitis NRRL Y-7124 was evaluated using a semi-defined fermentation medium
containing 90 g/l xylose. The assays were carried out in a bioreactor at 30°C,
under different aeration conditions (0.5, 1.0, and 1.5 vvm) and stirring rates
(200, 300 and 400 rpm) which resulted in KL
a values of 2.3, 18.7 and 65.8 h-1
respectively. According to the results, the bioconversion was dependent
on the aeration rate employed, the highest ethanol production (27.1 g/l)
being achieved when using a KL
a of 2.3 h-1. The increase of this parameter
to 18.7 and 65.8 h-1 promoted decreases of 52% and 100% on ethanol
production, respectively. By using a KL
a of 65.8 h-1 the ethanol production was
totally deviated to biomass production. Such results are of interest for the
development of a suitable technology for ethanol production by Pichia stipitis