Mathematical modeling of citric acid production by repeated batch culture

A mathematical model has been created for the process of citric acid biosyn thesis by yeast (mutant strain Yarrowia lipolytica) cultivated by the repea ted batch (RB) method on ethanol under conditions of nitrogen limitation. T he model accounts for cell growth as a function of nitrogen concentration i n the culture liquid; nitrogen uptake by growing cells; citric acid product ion; pH control in the fermenter by means of NaOH addition: and changes in system volume. The model represents a system of five nonlinear differential equations. Experimental measurements of cell concentration, citric acid co ncentration, and cultivation broth volume were used with the least squares method to determine the values of eight model parameters. The parameter val ues obtained were consistent with literature data and general concepts of c ell growth and citric acid biosynthesis. The model has been used to predict optimum RB culture conditions. (C) 2000 Elsevier Science Inc. All rights r eserved.