Improving Aspergillus niger seed preparation and citric acid production by morphology controlling-based semicontinuous cultivation

Abstract

Citric acid is an important platform chemical that is mainly produced by submerged fermentation of Aspergillus niger. However, seed preparation and citric acid production of Aspergillus niger under the current process are both inefficient. In this study, a semicontinuous seed cultivation process was constructed by controlling the morphology of Aspergillus niger. The results of this study indicated that direct re-use of mycelium pellets lead to a rapid drop in both pellet quantity and rate of citric acid formation. Using morphology-based mycelium pellet dispersion, biomass remained at 95.1% after 38 cycles (468 h) with improved citric acid production. Size of mycelium fragments, incubation time, and segmentation proportion were treated as key factors to affect the steady-state of semicontinuous cultivation. The new technique saved over half of the seed preparation time and reduced spore usage to 1/38 that of the conventional batch seed culture. The small mycelium pellets formed from dispersed mycelium fragments also exhibited improved citric acid yield and productivity in the pilot-scale fermentation. Specifically, the rate of citric acid productivity increased by 19.3%. Finally, the citric acid concentration reached 193.4 g/L on a 5000 L production scale. This technique provides a valuable reference for production process optimization using filamentous fungi.