Fermentation Process Monitoring through Measurement of Aerosol Release

Abstract

Fermentation involves many complex biological processes, some of which can be difficult to monitor. In this study, aerosol measurement was explored as an additional technique for monitoring a batch aerobic fermentation process using Escherichia coli strain W3110. Using this technique, a small aerosol extraction flow from the fermentor was continuously dried in‐line and analyzed with an aerosol size spectrometer and an aerosol photometer, used to measure the size‐integrated aerosol concentration. The results of the measurements demonstrated that the bacterial growth rate and the aerosol number concentration changed in a similar fashion: the effluent aerosol number concentration increased during the exponential growth phase and subsequently decreased after the bacterial cell concentration had reached a stable level. This aerosol concentration increased sharply approximately 1 h after initiation of growth. Thus, this increase in aerosol concentration suggests that the release of aerosols changes as a function of the microbial product formation activity. The products may change the rheological properties of the liquid, especially if surface‐active compounds are produced. The increase in aerosol concentration corresponds to a decrease in the values of the measured surface tension during the same time frame. Furthermore, the aerosol size spectrometer and the photometer showed similar time traces of the effluent aerosols. The size distributions of the solid residues from the fermentation broth remained relatively constant, while the concentrations changed with the phase of fermentation. As the photometer is inexpensive, it appears promising as a convenient instrument for monitoring fermentation processes.

Monitoring of Submerged Bioprocesses

“…The interpretation of these variables has to be made carefully in order to derive relevant information (Dixon and Kell, 1989;Royce, 1992). Other less frequently used properties that have been correlated to metabolic activity include: capacitance measurement (Fehrenbach et al, 1992;Austin et al, 1994;Mataguihan et al, 1994), measurements based on the heat evolution (Larson et al, 1993), osmotic pressure (Aoyagi et al, 1995), viscosity (Groot et al, 1991, vapor in the head space of the bioreactor (Gardini et al, 1997), filtration properties (Oolman et al, 1991;Mohseni and Allen, 1995), agitator speed (Lee et al, 1996), and the amount of aerosol release (Huang et al, 1994). Product concentration has also been estimated using indirect measurements, for example, Payot and Fick (1997) used conductivity measurements for lactic acid monitoring in fedbatch lactic acid production processes.…”