Optimising medium chain carboxylate production in xylan mixed-culture monofermentation

This work investigates the optimization of medium-chain carboxylate (MCC) production through xylan mixed-culture monofermentation. The pH screening in batch assays showed that the hydrolysis stage and selectivity towards MCC precursors were optimised at pH 6. Subsequently, a continuous stirred tank reactor (CSTR) and a Sequential Batch Reactor (SBR) were operated at different Hydraulic Retention Times (HRT), revealing that the SBR at HRT 2 days yielded the highest caproic acid since lactic acid availability and chain elongation process were balanced. An enriched medium with yeast extract and vitamins favoured the growth of chain elongators, and therefore, the MCC production. Moreover, cross-feeding interaction between bacteria in xylan fermentation was observed, and Pseudoramibacter was present in the highest caproic acid yields. This work highlights the impact of selecting the proper operational window to optimise one-stage MCC production.