Synergistic positive effect of organic acids on the inhibitory effect of phenolic compounds on Acetone-Butanol-Ethanol (ABE) production

Abstract

The synergistic effect of potential inhibitory compounds (organic acids and phenolic compounds) on ABE fermentation was studied with model media containing sucrose and real media prepared from beet and cane sugar refining molasses.The presence of phenolic compounds inhibited ABE fermentation at concentrations as low as 0.5g/L for gallic acid and 0.1g/L for catechin. The co-presence of organic acids (2.2g/L acetic, 1.8g/L lactic and 0.6g/L formic) showed a synergistic positive effect that can counteract the inhibitory character of phenolics. This effect was significantly higher at low phenolic concentrations. This means that the inhibitory effect of phenolic compounds on ABE production with Clostridium beijerinckii could be overcome by the presence of organic acids at low concentration in fermentation media.The results were confirmed by using a substrate of molasses. Better fermentation was achieved with beet molasses due to the lower concentration of phenolics, especially catechin. The fermentation using beet and cane sugar refining molasses as substrate (60g/L) provided an ABE yield of 0.40g ABE/g sugars and 0.31g ABE/g sugars, respectively and ABE concentrations of 12.3g/L (205g ABE/kg beet molasses) and 7g ABE/L (120g ABE/kg cane molasses).