• Aspergillus niger;
  • gluconic acid;
  • submerged fermentation;
  • semisolid-state fermentation;
  • surface fermentation;
  • solid-state surface fermentation


The production of gluconic acid with respect to varying substrate concentrations in submerged (SmF), semisolid-state (SmSF), surface (SF), and solid-state surface (SSF) fermentations was analyzed. Under the various fermentation conditions the biomass and specific growth rate varied with different concentrations of glucose. The highest level of gluconic acid (106.5 g dm−3) with 94.7% yield was obtained under SSF conditions. In all cases the maximum degree of gluconic acid conversion was observed at on initial substrate concentration of 120 g dm−3. The rate of glucose uptake increased on increasing the initial glucose concentration and glucose utilization was observed to be highest (89–94%) in the SmSF process and was comparable with the SSF and SF processes. The maximum rate of cell growth was obtained in all processes at an initial glucose concentration of 120 g dm−3. The gluconic acid production and change in pH were analyzed at varying time intervals and it was observed that the SmF and SmSF processes were completed within 6 days of incubation whereas the highest yield was observed after 12 days of incubation and continued thereafter in the SSF process.

© 2003 Society of Chemical Industry