93 IDENTIFICATION OF YIELD COEFFICIENTS IN A BAKER’S YEAST MODEL AN OPTIMAL EXPERIMENTAL DESIGN APPROACH C. ROCHA and E.C. FERREIRA Departamento de Engenharia Biológica Universidade do Minho Campus de Gualtar 4710 Braga Portugal e-mail: ecferreira@deb.uminho.pt http://www.deb.uminho.pt ABSTRACT The main objective of this work is to elaborate methodologies that allow the identification of yield coefficients through complete measurements of the state. Experimental design strategies are proposed in order to optimize the richness of data coming out from the experiments, quantified by indexes related to the Fisher information matrix. The objectives of the experimental planning have been addressed in terms of the programming of input trajectories. The experimental planning is envisaged for baker’s yeast aiming at the computation of the substrate feed trajectories. KEYWORDS Baker's Yeast, Parameter Estimation, Yield Coefficients, Experiment Design, Optimization INTRODUCTION The dynamics of a reactor network in a stirred tank bioreactor can be described by the following mass balance equations written in the matrix form: d dt Kr D U ξ ξ ξ = − + () (1) where ξ is the vector of the n component concentrations, K is the matrix of yield coefficients, r is the vector of reaction rates, U is the vector of feed rates and of gaseous outflow rates, D is the dilution rate. The reaction network for baker’s yeast (Saccharomyces cerevisiae) growth on sugar with ethanol production /consumption is usually [1] described by the following three metabolic pathways: Respiratory growth on sugar: k S + k C r X + k P 1 5 1 7 → Fermentative growth on sugar: kS r X + k P + k E 2 2 8 3 → Respiratory growth on ethanol: k E + k C r X + k P 4 6 3 9 → where S, C, X, P, E represent sugar (glucose), oxygen, yeast, carbon dioxide, and ethanol respectively, r 1 , r 2 , r 3 , are the reaction rates. These reactions are autocatalytic since yeast are self-reproducing microorganisms. The yield coefficients k i are expressed with respect to the production of 1 unit of yeast in each reaction.