of living bacteria in medium with 2 mM ferulic acid
was 32.1 × 10
6
cells/mL, while the reference medium
without ferulic acid only contained 23.4 × 10
6
cells/mL.
This was not due to a buffering effect, as the pH decreased
to 2.8 in all the media (Figure 3B). The concentration of
ferulic acid did not change very much during the cultiva-
tion (Figure 3D). Most cultures exhibited a decline in the
concentration of ferulic acid at the end of the cultivation,
but it is not clear that it was significant.
Results obtained with vanillin are shown in Figure 4
and in Table 1. Figure 4 indicates that vanillin did not
severely inhibit the growth of
G. xylinus
until the concen-
tration exceeded 2.5 mM (Figure 4A-C). An initial vanillin
concentration of 0.5 mM hardly affected glucose con-
sumption, pH value or BC yield (Figure 4 and Table 1).
With an initial vanillin concentration of 2.5 mM, the
glucose consumption rate declined from 3.5 g/(L
∙
d) to
1.7 g/(L
∙
d) (Table 1A). The concentration of living bacteria
at the end of the cultivation was 4.0 × 10
6
cells/mL, much
lower than in the cultures with reference medium, which
reached 23.4 × 10
6
cells/mL (Figure 4C). The volumetric
yield of BC declined as the concentration of vanillin in-
creased (Table 1B). When the initial concentration of van-
illin was 5 mM or higher, the glucose consumption rate
was <0.4 g/(L
∙
d) (Table 1A), the concentration of living
bacteria in the cultures was very low (Figure 4C), and
the yield of BC was <0.4 g/L (Table 1B).
The vanillin content in cultures with initial concentra-
tions of 0.5 or 2.5 mM seemed to decrease during the cul-
tivation (Figure 4D). Control experiments (with vanillin in
the medium but without bacterial inoculation) showed no
product formation making it plausible that conversion
products detected in bacterial cultures would be the result
of a biotransformation. Only very small concentrations of
การแปล กรุณารอสักครู่..