the cell membrane. Therefore, the concentrations of the
toxic form of the carboxylic acids may initially have been
lower than in comparable experiments with the aldehydes,
which agrees with the observation that the effect
on the cultures was less obvious for the acids.
G. xylinus was rather sensitive to vanillin, since growth
and BC production were almost completely inhibited
already at a concentration of 5 mM. This can be compared
with the S. cerevisiae strain BY4743, the growth of which
was inhibited by approx. 50% when the concentration of
vanillin was 5 mM [33]. Coniferyl aldehyde was more
inhibitory than vanillin though both of them have only
one aldehyde group. However, coniferyl aldehyde has an
unsaturated bond in its propanoid backbone (Figure 1A).
This structure has been reported to be a major contributor
to the inhibitory effect of phenolic compounds on S.
cerevisiae [18,34], and in accordance with our results this
observation appears valid also for G. xylinus.
The concentrations of vanillic acid in the G. xylinus
cultures were very low (