BACKGROUNDPotential inhibitory effects of byproducts from lignocellulosic hydrolysis process, including furfural and 5-hydroxymethyl furfural (HMF), on butyric acid fermentation by Clostridium tyrobutyricum were studied by adding furfural (0, 0.3, 0.6, 0.9 and 1.2g L-1) and HMF (0, 0.6, 1.2, 1.8 and 2.4g L-1) separately into the xylose medium. RESULTSIncreases in furfural or HMF concentration led to reduced butyric acid productivity. Delays on cell growth and xylose consumption were also noticed with increasing concentrations of furfural and HMF. Complete inhibition of C. tyrobutyricum fermentation was observed at 1.2g L-1 of furfural, while HMF showed less severe effects, and that C. tyrobutyricum could tolerate up to 2.4g L-1 of HMF. Both furfural and HMF could be metabolized by C. tyrobutyricum. CONCLUSIONFurfural at concentrations higher than 0.3g L-1 and HMF at concentrations higher than 0.6g L-1 can significantly inhibit the butyric acid fermentation of C. tyrobutyricum, and furfural had more severe effects in terms of cell growth and metabolisms. (c) 2017 Society of Chemical Industry