Biomass estimation using fluorescence measurements in Pichia pastoris bioprocess

The utilisation of tryptophan fluorescence as an indirect biomass measurement for the yeast Pichia pastoris, an excellent host system for the production of heterologous proteins, is presented. Direct fluorescence measurements for cell densities above 3 g dm-3 presented important interferences due to inner filter effects. To overcome this drawback, a dilution protocol is provided which allows the quenching of the emission signal caused by solid particles to be controlled. The measured tryptophan fluorescence intensities were used to estimate biomass concentration during a P pastoris batch bioprocess growing either on glycerol or methanol. The best measurement model tested was based on the application of a Luedeking-Piret-based equation to fluorometric measurements. Thus, a linear relationship between the specific fluorescence evolution rate and specific growth rate was applied. The mean absolute relative prediction error (MARE) for biomass concentration was about 6%. © 2005 Society of Chemical Industry.