Synthesis of medium-chain fatty acids from corn stover by sequential fermentation based on substrate configuration and initial pH optimization

Abstract

This work describes a novel sequential fermentation method for the production of medium-chain fatty acids (MCFAs) from corn stover, without adding exogenous electron donors/acceptors. The effects of the carbon substrate concentration, ethanol-to-acetate ratio (ED/EA), and initial pH on carbon chain elongation (CCE) by Clostridium kluyveri to produce MCFAs are investigated using ethanol and acetate as the electron donor and acceptor, respectively. A carbon substrate concentration of 300 mM C is sufficient for CCE. An initial weakly alkaline environment significantly enhances the production of caproate through buffering effects and by reducing inhibition of product formation. The maximum caproate production reached 4.41 g/L (initial pH 8.5; 300 mm C; ED/EA = 1:1). The ability of corn stover to generate a suitable ED/EA via two-step fermentation to synthesize MCFAs is also explored. Ultimately, 5.53 g/L butyrate and caproate can be obtained from corn stover, where caproate accounts for 2.79 g/L. This study offers innovative ideas for the sustainable production of bio-based chemicals.