t L-Malic acid and fumaric acid are C4 dicarboxylic
organic acids and considered as promising chemical building
blocks. They can be applied as food preservatives and
acidulants in rust removal and as polymerization starter units.
Molds of the genus Aspergillus are able to produce malic acid
in large quantities from glucose and other carbon sources. In
order to enhance the production potential of Aspergillus
oryzae DSM 1863, production and consumption rates in an
established bioreactor batch-process based on glucose were
determined. At 35 °C, up to 42 g/L malic acid was produced in
a 168-h batch process with fumaric acid as a by-product. In
prolonged shaking flask experiments (353 h), the suitability of
the alternative carbon sources xylose and glycerol at a carbonto-nitrogen
(C/N) ratio of 200:1 and the influence of different
C/N ratios in glucose cultivations were tested. When using
glucose, 58.2 g/L malic acid and 4.2 g/L fumaric acid were
produced. When applying xylose or glycerol, both organic
acids are produced but the formation of malic acid decreased
to 45.4 and 39.4 g/L, respectively. Whereas the fumaric acid
concentration was not significantly altered when cultivating
with xylose (4.5 g/L), it is clearly enhanced by using glycerol
(9.3 g/L). When using glucose as a carbon source, an increase
or decrease of the C/N ratio did not influence malic acid
production but had an enormous influence on fumaric acid
production. The highest fumaric acid concentrations were
determined at the highest C/N ratio (300:1, 8.44 g/L) and
lowest at the lowest C/N ratio (100:1, 0.7 g/L).