Continuous Production of Polygalacturonases (PGases) using Aspergillus niger in a Surface Culture Bioreactor and Modeling the Process

The feasibility of continuous production of PGases by a strain of Aspergillus niger was investigated in a surface culture bioreactor. Pectin was used as the substrate. The fermentation started in batch mode until the medium was covered with the mycelia of the microorganism and after that it turned to continuous mode by introducing the fresh feed. The process continued for 34 days. The thickness of the microorganism layer on the surface of the liquid medium became almost constant after about 1 week. The production of PGases, however, continued throughout the experiment. Maximum exo-polygalacturonase (exo-PGase) and endo-polygalacturonase (endo-PGase) activities of 1.5 and 0.014 U/mL were obtained, respectively. An increase in enzyme concentrations was observed when a similar system was used with a line for medium recycle. A Michaelis-Menten type equation was considered for the rate of PGases production in the surface culture bioreactor and the process was modeled. The model parameters were estimated using an optimization method (Particle Swarm Optimization). The model predicted the experimental data reasonably well.