Automated monitoring of amino acids during fermentation processes using on-line ultrafiltration and column liquid chromatography: application to fermentation medium improvement

An automated system for the monitoring of amino acids during fermentation processes is described and evaluated. The system is based on the on-line combination of a hollow-fibre ultrafiltration module, for the removal of cellular and macromolecular material from the broth, and ion-exchange chromatography with post-column o-phthalaldehyde derivatization, for determination of amino acids in the filtrate. As the complete sampling system can be steam-sterilized together with the fermenter, use of the monitoring system does not increase the risk of infection. The method is used to study the amino acid metabolism of a recombinant Escherichia coli, cultured on a complex nitrogen source. Monitoring of the 24-h fermentation can be performed unattendedly and the analysis frequency of once per hour provided detailed information with regard to the consumption of 15 amino acids. Subsequent improvement of the fermentation medium led to an increase in productivity of ca. 35%. In addition, preliminary results about the monitoring of peptides during this fermentation are reported.