Lignocellulosic biomass fermentation inhibitors

Phenolic compounds from lignin degradation, furan derivatives (furfural and HMF) from sugar degradation and aliphalic acids (acetic acid, formic acid and levulinic acid) are considered to be fermentation inhibitors generated from pretreated lignocellulosic biomass (53). The formation of these inhibitors depends on the process conditions and the lignocellulosic feedstocks 54). Various methods for detoxification of the hydrolyzates have been developed (55). These include... 

It was established that a range of concentrations exists in which fermentation inhibitors derived from pretreatments of lignocellu-losic feedstocks are not affecting the yeast, but will inhibit further growth of lactic acid bacteria. By an optimization of the levels of fermentation inhibitors the fermentation of biomass can be conducted under non-sterile conditions. Here, the yield of ethanol is comparable to those achieved under sterile conditions (22). Optimized inhibitor levels can be achieved by controlling the ratio of water to biomass of a lignocellulosic biomass during and after the pretreatment. 

R. oryzae strains have several advantageous characteristics, including the ability to directly utilize non-pretreated cellulose and hemicellulose, tolerance to the inhibitors present in acid hydrolysates of lignocellulosic biomass, and the ability to produce fumaric acid, a four-carbon unsaturated dicarboxylic acid [57]. Recently, the white rot fungus Trametes hirsute was shown to be capable of directly fermenting starch, wheat bran, and rice straw to ethanol without prior acid or enzymatic hydrolysis [58]. 

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