To the best of our knowledge,
it is the first time that the functionality
of the TCA cycle and glyoxylate shunt during wheat bread dough fermentation
is studied. Despite various reports on the functionality of
the reductive pathway of the TCA cycle during anaerobic fermentation,
we found no evidence for activity in this pathway during dough fermentation.
By contrast, deletion of the genes responsible for the oxidative
pathway of the TCA cycle and the glyoxylate shunt strongly affected
the fermentation rate of yeast and the succinic acid levels produced during
dough fermentation. Although the TCA cycle genes are likely downregulated
during dough fermentation due to the presence of high sugar
levels and the apparent anaerobic conditions in dough, deletion of the
genes responsible for important enzymes in this cycle led to significant
changes in the level of succinic acid during dough fermentation, suggesting
at least a basal level of activity in the TCA pathway.
Despite significant changes in the level of succinic acid produced by
various mutants, the dough pH did not show significant changes, probably
due to the buffering capacity of dough. As a result, the changes in
the levels of succinic acid did not impact the gas holding capacity of
dough. Part of this result might be due to the relatively low level of
succinic acid produced by the S288C laboratory strain used in this
study. Indeed, previous studies have shown that commercial strains
produce four times more succinic acid than this laboratory strain. It
might therefore be interesting to knock out the promising genes