7-14: Validating Raman spectroscopy as a method for measuring sugars to acetic acid fermentation

Quantification of carbohydrates and bioproducts can be a bottleneck in a bioconversion process. On-line analytical measurements that rapidly monitor all processes could be an important means of increasing conversion efficiencies. Compared to currently utilized analytical techniques, Raman spectroscopy (RS) is distinct because many analytes in the sample can be measured simultaneously in real time. Raman analysis of sugars present in lignocellulosic biomass as well as typical bioconversion products like ethanol and acetic acid have shown that each analyte exhibits Raman stretching  in a distinct “fingerprint” region of the collected spectrum. Principle component analysis (PCA) can then be used to determine the relative amounts of each analyte, followed by partial least squares modeling with a validation dataset. Fermentation reactions using pure glucose and steam exploded switchgrass hydrolysate have already demonstrated the ability of RS to measure glucose consumption and ethanol yield in real time.

In this paper we investigate the utilization of Raman spectroscopy for online monitoring of carbohydrate consumption and acetic acid production by the homoacetogen, M. thermoacetica (Clostridium thermoaceticum), ATCC 39073, from synthetic glucose, xylose, and steam exploded hybrid poplar hydrolyzate. M. thermoacetica is a thermophilic obligate anaerobe that can homoferment both pentose and hexose sugars to acetic acid using CO₂ as an electron acceptor, at temperatures between 55 and 60°C and pH 6.5-6.8. We will present the quantification of xylose, glucose and acetic acid by RS in real time during fermentation, and define a general model for acetic acid fermentation based on real time analysis.