Hydrothermal pretreatment and enzymatic saccharification of corn stover for efficient ethanol production

Corn stover used in this study contained 37.0 ± 0.4% cellulose, 31.3 ± 0.6% hemicellulose and 17.8 ± 0.2% lignin on dry basis. Hydrothermal pretreatment and enzymatic saccharification were evaluated for conversion of corn stover cellulose and hemicellulose to fermentable sugars. Under the optimum conditions of hydrothermal pretreatment of corn stover (10%, w/v; 200 °C; 5 min) and enzymatic saccharification (45 °C, pH 5.0, 72 h), a total of 550 ± 5 mg of fermentable sugars was obtained per g corn stover which is equivalent to 72% of theoretical sugar yield. The corn stover hydrolyzate was fermented without any detoxification by recombinant Escherichia coli strain FBR 5 at pH 6.5 and 37 °C for 74 h to produce 20.9 ± 0.5 g ethanol from 42.8 ± 1.7 g sugars per L with a yield of 0.49 g ethanol per g available sugars and 0.27 g ethanol per g corn stover which is equivalent to 68.7% of theoretical ethanol yield from corn stover. This is the first report on the production of ethanol from hydrothermally pretreated corn stover by the recombinant bacterium.

► Yield of total sugars from corn stover (100 g/L) is 55 g/L.
► Hydrothermal pretreatment is highly effective for enzymatic corn stover hydrolysis.
► Recombinant Escherichia coli FBR5 produces ethanol from hydrolyzate without detoxification.
► The ethanol yield was 0.27 g/g corn stover which is 69% of theoretical yield.