Lignin Impact on Fiber Degradation. 3. Reversal of Inhibition of Enzymatic Hydrolysis by Chemical Modification of Lignin and by Additives

The impact of lignins of various origins on filter paper hydrolysis by fungal cellulase was evaluated. Powdered lignins were added to enzyme incubations, either as isolated or after thorough hydroxypropylation of phenolic sites. Extent of cellulose hydrolysis was reduced by 14−60% by the addition of up to 15% lignin to the substrate. Unmodified lignins were more detrimental to cellulose hydrolysis than hydroxypropylated lignins. The inhibitory effect of lignin addition was only partially overcome by a 10-fold increase in cellulase activity, suggesting inhibitory lignin interactions with both substrate and enzyme. Preincubation of cellulase with underivatized lignins resulted in reduced enzyme activity and soluble protein concentration in the supernatant, suggesting protein precipitation with lignin rather than reduced activity of a lignin−enzyme complex as the inhibitory mechanism. Two further experiments showed that the negative impact of lignin on cellulose hydrolysis can be counteracted by addition of various N compounds and by ammoniation. Keywords: Lignin; cellulose degradation; cellulase inhibition; free phenolic group; ammoniation; PEG; PVP; N compounds