Fed-batch culture implies low levels of substrate concentration
during the course of fermentation, while ethanol is
accumulating in the medium. This type of cultivation
regime, along with the cell recycling, is the most employed
technology in Brazil for bioethanol production due to the
possibility of achieving higher volumetric productivities.
Control of the flow rate of medium feed is quite advantageous
because the inhibitory effect caused by high substrate
or product concentrations in the fermentation broth can be
neutralized. It was observed that the addition of sucrose in
linear or exponentially decreasing way leads to 10–14%
increase in ethanol productivity (Echegaray et al., 2000).
The optimization of feeding policy plays a crucial role for
increasing both productivity and ethanol yield of fed-batch
fermentations. This issue was analyzed in a previous review
(Cardona and Sa´nchez, 2007). For fed-batch cultures, Alfenore
et al. (2004) showed that higher ethanol concentrations
(147 g/L) can be obtained in cultures without oxygen limitation (0.2 vvm) during only 45 h in comparison
to microaerobic conditions