Figure 4. Effect of different initial pH on the production of citric acid by Aspergillus niger GCMC-7 in stirred fermentor.

Sugar added: 150 g/l.
Agitation intensity: 200 rpm.
Air supply: 1.0 l/l/min.
Incubation temperature: 30ºC.
Fermentation period: 144 h.
The error bars indicate the standard deviation among the three parallel replicates.