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Simultaneous synthesis of lactic acid and hydrogen from sugars via capnophilic lactic fermentation by Thermotoga neapolitana cf capnolactica

Pradhan, Nirakar; d'Ippolito, Giuliana; Dipasquale, Laura; Esposito, Giovanni; Panico, Antonio; Lens, Piet N.L.; Fontana, Angelo

This study investigated the effect of the salinity level, buffering agent and carbon source on the hydrogen (H2) and lactic acid synthesis under capnophilic (CO2-assisted) lactic fermentation (CLF) by Thermotoga neapolitana cf capnolactica (DSM 33003). Several series of batch fermentation experiments were performed either in 0.12 L serum bottles for selection of the best performing conditions or in a 3 L fermenter for the best possible combination of conditions. The serum bottle study revealed that change in the salinity level of the culture medium from 0 to 35 g L−1 NaCl increased lactic acid synthesis by 7.5 times without affecting the H2 yield. Use of different buffers (MOPS, TRIS or HEPES) did not affect the average H2 yield of 3.0 ± 0.24 mol H2 mol−1 of glucose and lactic acid synthesis of 13.7 ± 1.03mM when the cultures were sparged by CO2. Among the carbon sources investigated, glucose was found to be the best performing carbon source for the CLF fermentation with 35 g L−1 of NaCl and 0.01M of phosphate buffer. Hence, an up-scale experiment using a 3 L fermenter and the combination of the best performing conditions showed a 2.2 times more lactic acid synthesis compared to the 0.12 L serum bottle experiments. The study reveals the robustness and flexibility of the CLF-based technology using T. neapolitana cf capnolactica fermentation under various operating environmental conditions.

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