Fundamental investigations on the near-infrared spectra of microbial biomass as applicable to bioprocess monitoring

The near-infrared (NIR) spectrum of microbial biomass was studied for a range of microorganisms, with relevance to applicability in bioprocess monitoring and control. Three experiments were carried out to investigate the validity of measuring biomass using NIR spectroscopy (NIRS). (1) A comparative study of the NIR reflectance spectra of five representative microorganisms, of interest in a bioprocessing context, showed that the spectral signature of biomass, with respect to the wavelength regions, is essentially identical for all five microorganisms. The signature wavelengths are listed. (2) The spectral signature correlated well quantitatively with dry cell mass measurements, when the biomass of a filamentous microorganism was isolated from its matrix and analysed. The observation was clearer with reflectance measurements of dried biomass than with transmittance measurements of aqueous suspensions. (3) The biomass reflectance spectral signature remained the same at different culture ages of Penicillium chrysogenum, and showed quantitative correlation with dry cell mass measurements at the relevant wavelengths. This study therefore indicates those spectral regions which are Likely to be the basis for quantitative modelling of microbial biomass in bioprocesses using NIRS, regardless of the microbial type and the culture age.