A novel real-time method to estimate volumetric mass biodensity based on the combination of dielectric spectroscopy and soft-sensors

BACKGROUND The PAT initiative encourages designing, analyzing, and controlling manufacturing through timely measurements. Dielectric measurements and first principle soft-sensors emerged as valuable real-time bioprocess analytical PAT tools to improve process understanding and control capabilities. RESULTS The estimation of a novel physiological variable, bio-density is presented, using a combination of two PAT sensors, dielectric spectroscopy and a soft-sensor based on first principle elemental balances. Within this contribution, calibrations for the estimation of biomass dry weight using dielectric measurements were found to change in the transition from batch- to fed-batch and within the induction phase for two recombinant E. coli bioprocesses. This was explained by a change in cell size, as indicated by flow cytometric measurements, light microscopy and changes in the beta dispersion dielectric spectrum. Biomass dry weight was accurately determined using a first principle soft-sensor. The combination of both signals allowed the real-time estimation of a new physiological variable, interpreted as bio-density. Applying this concept, batch/fed-batch and induction phase physiological changes were successfully observed in real time. Furthermore, a correlation with the specific product titer was observed. CONCLUSION This contribution enhances the application spectrum of dielectric measurements and soft-sensors for the detection of physiological changes and recombinant product estimation, aiming at more efficient design, monitoring and control of bioprocesses as demanded by the process analytical technology (PAT) initiative. © 2014 Society of Chemical Industry