On-line bioprocess monitoring with a multi-wavelength fluorescence sensor using multivariate calibration

Cultivations of Pseudomonas fluorescens were monitored with a multi-wavelen gth on-line fluorescence sensor. The multi-wavelength fluorometer used exci tation light from 270 to 550 nm with 20 nm steps and measured fluorescence emission from 310 to 590 nm. The fluorescence, on-line exhaust gas measurem ents and off-line analysis of nitrate, succinate, optical density and prote in were compared chemometrically by multivariate calibration, i.e. computin g partial least square (PLS) regression models. Based on the multivariate r egression models, it was possible to determine CO2 and O-2 composition in t he exhaust gas (the correlation coefficients, R-2 between the predicted val ues by the PLS model and the measured values was 0.97 for CO2 and 0.97 for O-2, respectively). Also to make quantitative determinations of succinate ( R-2 = 0.97), protein (R-2 = 0.94), optical density (R-2 = 1.0) and nitrate (R-2 = 0.98) in the medium based on the fluorescence spectra. Only a limite d data set was available but the results indicated that the sensor could in directly determine non-fluorescent compounds, i.e. nitrate and succinate, w hich probably is due to the stoichiometric relationship between fluorescent cellular components and non-fluorescent compounds. Consequently multi-wave length fluorescence is an interesting technique for a wide range of applica tions. (C) 2001 Elsevier Science B.V. All rights reserved.