On-line Estimation of Fermentation Parameters in Bioreactor Cultures of Aspergillus terreus for Itaconic Acid Production

Important fermentation parameters were estimated by use of a vent gas analyzer for oxygen in the computer-controlled bioreactor cultures of Aspergillus terreus, a producer of itaconic acid utilized as a co-monomer for manufacturing various polymers such as rubbers, paints, and chemical resins. Specifically, quantitative correlations between cell growth rate, oxygen uptake rate (OUR) were obtained in A. terreus fermentations. OUR, a critical indicator of the producers' activities, and oxygen mass transfer rate (k_La), a crucial parameter for bioprocess scale-up, were calculated on-line by applying oxygen mass balance. In addition, by dividing the oxygen uptake rate (OUR) by the total oxygen consumed, on-line estimation of the cells specific growth rate (μ), which is a very important parameter for the diagnosis of biosynthetic pattern of secondary metabolite such as itaconic acid, was successfully carried out. It was also possible to estimate cell concentration directly by use of oxygen-cell yield (Y_x/o) which was obtained based on a correlation between cell growth and total oxygen consumed. In addition, an efficient and stable bioprocess was established for enhanced production of itaconic acid through automatic control of dissolved oxygen in a cascade mode with almost 95% accuracy.