Aspergillus niger fermentation is the main way for the industrial production of citric acid. Modeling of Aspergillus niger from the perspective of cybernetics is significant for better understanding the metabolic behavior of this industrial microorganism. The metabolic pathways in Aspergillus niger during citric acid fermentation are investigated. Based on the simplified metabolic network

a cybernetic model describing the balance of intracellular metabolites and enzyme levels is constructed. Meanwhile

a first-order closed-loop regulator model is used to describe the transient enzyme pool establishment shortly after the inoculation. Combining with the bioreactor model

it is found that model simulations of intracellular enzyme concentrations are in coincidence with the measurements qualitatively

while the macroscopic state variables (biomass concentration

substrate concentrate and product concentrations) agree well with the offline assays.