Microbial saccharification of wheat bran for bioethanol fermentation

Abstract In this study, effects of various strains from different genera - Aspergillus, Penicillium, Rhizopus, Mucor and Trichoderma - and of their multi-cultural fungal consortium on bio-pretreatment of wheat bran were investigated. The highest soluble carbohydrate content (198.8 mg/g) was released by P. chrysogenum F.00814 strain after 3–5 days of pretreatment. The combination of A. niger F.00632 and T. viride F.00795 strain resulted in 191.9 mg/g soluble carbohydrate that increased to 195.82 g/L by the consortium of A. niger NCAIM F.00632, P. chrysogenum NCAIM F.00814 and T. viride NCAIM F.00795 strains after three days. Optimal ratio of liquid to solid, pH and temperature as well as inoculum ratio were determined to be 5:1, pH 5.0, 30 °C and 65:25:15% in total 107 conidia (of A. niger, P. chrysogenum and T. viride) per gram dry substrate, respectively. The application of fungal multi-cultures resulted in about 58.8 g soluble carbohydrate from 100 g substrate after 3 days of bio-treatment meaning our concept should work. The ethanol fermentation of bio-pretreated wheat bran was carried out using S. cerevisiae Levuline Fb and K. marxianus NCAIM Y.00959 and Z. mobilis subsp. mobilis B.01327T strains in both modes’ mono- and multi-culture. 7.6% v/v was the maximum ethanol content obtained after 7 days of fermentation with mash containing 20% (w/v) initial reducing sugar when initiation with mixed cultures (S. cerevisiae and K. marxianus) and after two days the Z. mobilis subsp. mobilis B.01327T strain was added. These results were very promising to develop technology to produce lignocellulosic bioethanol.