Mathematical Modeling of Citric Acid Production and Microbial Growth Kinetics Using Aspergillus niger in Batch Fermentation

¹ Department of Biotechnology, Faculty of Applied Science, King Mongkut’s University of Technology North Bangkok, Wong Sawang, Bang Sue, 10800 Bangkok, Thailand
² Department of Cosmetic Science, Faculty of Science and Technology, Suan Dusit University, 10300 Bangkok, Thailand

^* Corresponding author: sasithorn.k@sci.kmutnb.ac.th, s660407181004@email.kmutnb.ac.th

Abstract

This study investigates the microbial growth kinetics and citric acid production by Aspergillus niger in batch fermentation, employing Monod, Logistic, and Gompertz models to analyze the dynamic relationships between biomass growth, substrate consumption, and citric acid formation. A series of experiments were conducted in a 5 L stirred tank batch bioreactor with 3 L working volume, using glucose (97 g/L) as the carbon source. Model predictions were validated using experimental data from batch fermentation runs. The results showed that A. niger exhibited typical microbial growth behavior, with biomass concentration increasing from 2.65 g cell/L at 0 hours to a peak of 14.58 g cell/L at 192 hours, before declining to 12.39 g cell/L by the end of the fermentation. Citric acid production followed a similar trend, reaching a maximum of 24.75 g/L at 240 hours and subsequently declining. Model fitting results revealed that the Gompertz model provided the best fit and yield, maximum specific growth rate μ_max 15 h^-1 exhibiting the highest goodness-of-fit (R² = 0.989) compared to the Monod (R² = 0.974) and Logistic models (R² = 0.988). The Gompertz model effectively captured the S-shaped growth and product formation patterns, including the deceleration phase associated with nutrient depletion and product inhibition. This study highlights the effectiveness of the Gompertz model in describing the fermentation process and emphasizes the importance of model selection in evaluating fermentation performance and improving the understanding of citric acid production kinetics.