Applications: Full Spectral Data Collections

Optical measurements are frequently used to represent cell concentration, but a UV-VIS or VIS-NIR spectrometer provides more information than singular optical density measurements for micro-organisms. Cytoprom’s UV-VIS spectrometers can collect full spectral data for wavelengths between 200-850 nm and a VIS-NIR spectrometer from 350-1000 nm. Even on a simple visual basis full spectral data can be used as a fingerprint for quality control. An unexpected absorbance at a particular wavelength or the lack of an absorbance where one is expected can easily be visualised in a simple 3-D plot, such as the one shown below. Changes to standard profiles on repeated batch data can rapidly indicate a batch anomaly.

Advanced techniques for processing data of spectral scans, particularly in conjunction with NIR spectroscopy, are now being used to measure all manner of process variables on-line and in-situ. We believe our innovative solution could strongly enhance this avenue of interest in the near future. We can provide fiber-optic probes with a range of path lengths and Arnold and co-workers (Ref. 1) report that the path length of fiber optic probes used for NIR spectroscopy is a critical factor in accuracy. Furthermore, Tamburini and coworkers (Ref. 2) report that both agitation and aeration rates influences the spectral signals markedly. With NIRS measurements it is critical to avoid a high level of light scattering from the cell mass, because there is a relatively low concentration of analyte by comparison. Harvey and McNeil (Ref. 3) refer to this fact in their attempts to monitor biomass, ethanol, glucose and protein content simultaneously during high density fed-batch baker’s yeast production.

Selected spectral data showing signature characteristics at approximately 260 nm and 480 nm.

References

[1] Arnold, S. A., Gaensakoo, R., Harvey, L. M. & McNeil, B. (2002). Use of at-line and in situ near-infrared spectroscopy to monitor biomass in an industrial fed-batch Escherichia coli process. Biotechnology and Bioengineering 80, 405-413.

[2] Tamburini, E., Vaccari, G., Tosi, S. & Trilli, A. (2003). Near-infrared spectroscopy: A tool for monitoring submerged fermentation processes using an immersion optical-fiber probe. Applied Spectroscopy 57, 132-138.

[3] Finn, B., Harvey, L. M. & McNeil, B. (2006). Near-infrared spectroscopic monitoring of biomass, glucose, ethanol and protein content in a high cell density baker&rquo;s yeast fed-batch bioprocess. Yeast 23, 507-517.