Comparison of different methods for the detoxification of lignocellulose hydrolyzates of spruce

This study describes different detoxification methods to improve both cell growth and ethanol production by Baker's yeast, Saccharomyces cerevisiae. A dilute-acid hydrolyzate of spruce was used for the all detoxification methods tested. The changes in the concentrations of fermentable sugars and three groups of inhibitory compounds-aliphatic acids, furan derivatives, and phenolic compounds-were determined and the fermentability of the detoxified hydrolyzate was assayed. The applied detoxification methods included: treatment with alkali (sodium hydroxide or calcium hydroxide); treatment with sulfite (0.1% [w/v] or 1% [w/v] at pH 5.5 or 10); evaporation of 10% or 90% of the initial volume; anion exchange (at pH 5.5 or 10); enzymatic detoxification with the phenoloxidase laccase; and detoxification with the filamentous fungus Trichoderma reesei. Anion exchange at pH 5.5 or 10, treatment with laccase, treatment with calcium hydroxide, and treatment with T. reesei were the most efficient detoxification methods. Evaporation of 10% of the initial volume and treatment with 0.1% sulfite were the least efficient detoxification methods. Treatment with laccase was the only detoxification method that specifically removed only one group of the inhibitors, namely phenolic compounds. Anion exchange at pH 10 was the most efficient method for removing all three major groups of inhibitory compounds; however, it also resulted in loss of fermentable sugars.