Fig. 1 shows the impact of glycerol or glucose concentration (5–
40 g/L) as co-substrates on the lactobionic acid production from
cheese whey by P. taetrolens. Whereas the increase in glycerol concentration
was translated into higher volumetric lactobionic acid
productivities (0.52–0.70 g/L h) but similar specific production
rates (0.3–0.37 g/g h), biomass yield on glycerol was progressively
reduced (from 0.2 to 0.06 g/g with 5 and 40 g/L of glycerol supplementation,
respectively) notwithstanding the higher glycerol availability
in the fermentation broth (Fig. 1A). Bioconversion ability of
P. taetrolens cells was thus not enhanced in a whey/glycerol batch
co-fermentation at shake-flask scale, channelling the glycerol overflow
toward supporting non-producing lactobionic acid cells.
Moreover, the progressive reduction in biomass yield on glycerol
(YX/S) suggested that cells were unable to use all the C-source available
for cell biomass formation, leaving i.e. a high residual amount
of glycerol (20 g/L) in a whey/glycerol batch co-fermentation
with 40 g/L of glycerol.