Study of the bioprocess conditions to produce bioethanol from barley straw pretreated by combined soda and enzyme-catalyzed extrusion

Combined soda and enzyme-catalyzed extrusion pretreatment (bioextrusion) of barley straw was evaluated for bioethanol production. The effect of the enzyme dose on the bioextrudate was for the first time analyzed. The enzyme load (5–10 FPU/g DM) had a significant impact on the solubilization of sugars during bioextrusion and also affected the saccharification yield at long incubation times. The solids concentration (17–25% w/w) in the extended incubation of bioextrudates was also studied and its effect on the carbohydrate conversion and sugar release was evaluated. An enzyme dose of 10 FPU/g dry matter and a solids content of 20% (w/w) were selected as the best conditions to submit the bioextrudate to a liquefaction plus simultaneous saccharification and co-fermentation (LSSCF) process using a modified S. cerevisiae strain. At the end of the process, an ethanol concentration close to 38 g/l was obtained, corresponding to a production of 15.8 g ethanol/100 g raw barley straw.