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 meth ods tested. The changes in the concentrations of fermentable sugars and thr ee groups of inhibitory compounds-aliphatic acids, furan derivatives, and p henolic compounds-were determined and the fermentability of the detoxified hydrolyzate was assayed. The applied detoxification methods included: treat ment with alkali (sodium hydroxide or calcium hydroxide); treatment with su lfite (0.1% [w/v] or 1% [w/v] at pH 5.5 or 10); evaporation of 10% or 90% o f the initial volume; anion exchange (at pH 5.5 or 10); enzymatic detoxific ation with the phenoloxidase laccase; and detoxification with the filamento us fungus Trichoderma reesei. Anion exchange at pH 5.5 or 10, treatment wit h laccase, treatment with calcium hydroxide, and treatment with T. reesei w ere the most efficient detoxification methods. Evaporation of 10% of the in itial volume and treatment with 0.1% sulfite were the least efficient detox ification methods. Treatment with laccase was the only detoxification metho d that specifically removed only one group of the inhibitors, namely phenol ic compounds. Anion exchange at pH 10 was the most efficient method for rem oving all three major groups of inhibitory compounds; however, it also resu lted in loss of fermentable sugars.