Can biomass be measured in a fermentation process using ATR-FTIR spectroscopy Bacillus subtilis as an example

Biomass is an important parameter in fermentation processes. The estimation of biomass during fermentation usually uses an off-line method, such as optical density at 600 nm (OD600) or the determination of dry cell weight (DCW). Online measurement of biomass via mid-infrared (MIR) spectroscopy has also been published. However, no strict demonstration has been given that biomass measurement by MIR is due to the specific absorption of infrared radiation by cells. Three factors are analyzed about cell absorption, which being: optical sampling theory, spectral absorbance intensity inspection, and PLS regression of cells model. Three aspects lead to the conclusion that the measurement of biomass by MIR is not due to specific absorption by bacteria but rather to a chance correlation with the substrate glutamate in this study. If a chance correlation is present, the biomass can be measured by this indirect method. The most reliable measurement method is still by DCW or OD600. It is frustrating that the online measurement of biomass still remains uncertain.