The Modeling And Validation Of Vitamin C Two-Step Fermentation Process

Production of Vitamin C (VC) is commonly carried out with two-step fermentation process. With the competition of VC market become more and more fierce, the realization of optimal control of such process and improvement of VC production have come into focus in recent years. Great progress has been made in the first step fermentation , so researchers are mainly focusing on improvement of VC productivity in the second step, which is the conversion of L-sorbose to 2-KGA. Mathematic model serves as the foundation of control process, and this paper mainly concentrates on the modeling of 2-KGA production process in the following field:The macrokinetic model of 2-KGA fermentation processThe 2-KGA fermentation process engages two kinds of bacteria which are Bacillus megaterium, usually called big bacteria, and Gluconobacter oxydans,usually called small bacteria. How to describe the relation between the two bacteria is the key point of modeling 2-KGA fermentation process. The culture supernatant of B. megaterium can enhance the proliferation of G. oxydans and the synthesis of 2-KGA. On the other hand, 2-KGA will lead to the dissolution of B.megaterium. In cell growth models of the two bacteria, the interaction between such two bacteria has been reflected through introduction of 2-KGA restraint item and B.megaterium concentration item respectively. Experimental results demonstrate that the model can describe the cell growth and the 2-KGA production with reasonable accuracy.Model of airlift reactorAirlift reactors are widely used in 2-KGA fermentation process. This paper introduces methods commonly used in modeling of such reactors and simulation of dissolved oxygen (DO) have been given. The simulation results show the axial inhomogeneities in steady-state DO in airlift bioreactors. The DO in the bottom section is generally higher the that in the top section.Synthesis of modelsThe combination of macrokinetic model and airlift model have been studied. The mathematical model of airlift is based on tanks-in-series model. The DO has been considered in the macrokinetic model of 2-KGA fermentation process. The simulation results show the differences between the top and bottom section in 2-KGA production rate and L-sorbose consumption rate, which demonstrates the effect of DO on 2-KGA fermentation process. It’s quite reasonable to improve 2-KGA productivity through the amelioration of reactor structure.