Improving Saccharomyces cerevisiae growth against lignocellulose-derived inhibitors as well as maximizing ethanol production by a combination proposal of γ-irradiation pretreatment with in situ detoxification

Four combined strategies of irradiation pretreatment with in situ detoxification, H2O rinsing, H2O/ethyl acetate (2:8, v/v) contacting, NaOH (1 mM, pH 11.0) overliming and NaBH4 (20 mM) reduction, were conducted to solve the toxicity dilemma in ethanol fermentation. The irradiated straw was characterized by FT-IR, SEM and AFM. The compositions of irradiation-mediated inhibitors formed during pretreatment were analyzed with GC–MS. The detoxified straw (200 gDS/L) was hydrolyzed with enzymes cocktails (∼1 mg protein/gDS) optimized by a 3-factor mixture design. The hydrolysate was bioconverted to ethanol with separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) using Saccharomyces cerevisiae. Results showed that glucose yield varied from 60% to 80% and xylose yield from 40% to 60% in dependence on detoxification methods. Yeast growth, residual glucose and ethanol yield varied with the combination approaches. The highest glucose bioconversion (99.7%) and ethanol yield (70%) were achieved via the combined proposal of irradiation pretreatment with NaBH4 detoxification regardless of SHF and SSF. The findings revealed that the combination proposal of irradiation pretreatment with NaBH4 detoxification in situ would be a promising alternative method for bioethanol production from liginocellulosic biomass.