Optical monitoring of chemical processes in turbid biogenic liquid dispersions by Photon Density Wave spectroscopy
In turbid biogenic liquid material, like blood or milk, quantitative optical analysis is often strongly hindered by multiple light scattering resulting from cells, particles, or droplets. Here, optical attenuation is caused by losses due to absorption as well as scattering of light. Fiber-based Photon Density Wave (PDW) spectroscopy is a very promising method for the precise measurement of the optical properties of such materials. They are expressed as absorption and reduced scattering coefficients (μ a and μ s′, respectively) and are linked to the chemical composition and physical properties of the sample. As a process analytical technology, PDW spectroscopy can sense chemical and/or physical processes within such turbid biogenic liquids, providing new scientific insight and process understanding. Here, for the first time, several bioprocesses are analyzed by PDW spectroscopy and the resulting optical coefficients are discussed with respect to established mechanistic models of the chosen processes. As model systems, enzymatic casein coagulation in milk, temperature-induced starch hydrolysis in beer mash, and oxy- as well as deoxygenation of human donor blood were investigated by PDW spectroscopy. The findings indicate that also for very complex biomaterials (i.e., not well-defined model materials like monodisperse polymer dispersions), obtained optical coefficients allow for the assessment of a structure/process relationship and thus for a new analytical access to biogenic liquid material. This is of special relevance as PDW spectroscopy data are obtained without any dilution or calibration, as often found in conventional spectroscopic approaches.
KeywordsPhoton Density Wave spectroscopy Enzymatic milk coagulation Beer mashing Human donor blood Process analytical technology Light scattering
We like to thank Anita Fuge for fruitful discussions and help with the milk experiments and Hans Scheuren for his help with the mashing experiments. We appreciate support by Hans Bäumler and Radostina Georgieva from the Institute for Transfusion Medicine, Charité Berlin. Furthermore, we like to acknowledge the financial support from the German Federal Ministry of Economics and Technology (grant no. 16IN0418) and the German Federal Ministry of Education and Research (grant no. 03Z2AN12).
The authors contributed differently to this paper: D.M. worked on the monitoring of the blood oxygenation, S.V.R. on enzymatic milk coagulation, and J.T. on beer mashing. R.H. and O.R. oversaw the experiments, and R.H. and D.M. wrote the manuscript.
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