Monitoring and control of processes in bioreactors is of great importance in biotechnology. The essential tasks in bioprocess monitoring are the determination of substrate uptake rate, specific growth rate of the organisms, and the product formation rate. Better monitoring of the production process enables more efficient, sustainable and controlled applications in pharmaceutical industry and biorefineries. Development on on-line analysis techniques reduces total analysis time because manual sample pretreatment steps are avoided. Also, random errors are reduced.

Filamentous fungi are common microorganisms in the fermentation industry for the large-scale production of proteins. Trichoderma reesei is able to produce and secrete large concentrations of proteins that are used as plant material hydrolyzing enzymes, especially amylases, proteases and cellulases.

The aim of this work was to develop and validate an on-line capillary electrophoresis setup to study extracellular protein production by Trichoderma reesei during bioreactor cultivation. The sample was filtered with a cross-flow filtration unit, and the permeate was used for analysis. A commercial capillary electrophoresis device was modified to work as on-line analysis device and a 500 µL flow-through vial was constructed. The capillary electrophoretic method employed UV detection to produce a fast and robust on-line analysis of proteins during a bioreactor cultivation of filamentous fungi.