In order to overcome the preferential oxidation of glucose over
lactose as well as the potential C-source catabolite repression in
P. taetrolens cells during batch mode, mixed carbon source strategies
with lactose/glucose/glycerol feedings in combination with a
pH-shift cultivation strategy at 6.5 were carried out (Fig. 3). As
can be seen in Fig. 3A, both glycerol and glucose feedings supported higher cell densities (1.7–1.8 g/L) in comparison to
those values achieved with lactose feeding (1.5 g/L) at the onset
of the stationary growth phase. These results suggested that fractions
of non-lactose C-sources (glucose and glycerol) were used
for cell biomass, promoting higher cell density conditions than
those achieved in a whey/lactose fed-batch co-fermentation.
As Fig. 3B shows, DOT became limiting at early growth phase
(