(447a) Stimulation and Inhibition of Organosolv Lignins on Enzymatic Hydrolysis Mediated By Zeta Potential and Hydrophobicity

Lignin typically inhibits enzymatic hydrolysis of cellulosic biomass, but certain lignin also enhances enzymatic hydrolysis. In this study, we examined the physicochemical properties and structures of ethanol organosolv lignins (EOL) from hardwood and softwood and ascertain the association between lignin properties and their inhibitory and stimulatory effects on enzymatic hydrolysis. The zeta potential and hydrophobicity of EOL lignin samples, isolated from organosolv pretreatment of cottonwood, willow, aspen, eucalyptus and loblolly pine, were determined and correlated with their effects on enzymatic hydrolysis of Avicel. EOLs from cottonwood (CW), black willow (BW) and aspen (AS) improved the 72 h hydrolysis yield by 8-12%, while EOLs from eucalyptus (EH) and loblolly pine (LP) decreased the 72 h hydrolysis yield by 6% and 16%, respectively. The results showed a vigorous correlation (y= 51.97-6.148 × hydrophobicity - 1.583 × zeta potential, r2=0.995) between the 72 h hydrolysis yield with hydrophobicity and zeta potential. The strong correlation indicated the hydrophobicity of EOL was a negative effect and the negative zeta potential of EOL was a positive effect. HSQC NMR spectra showed that β-O-4 linkages in lignin to react with ethanol to form an α-ethoxylated β-O-4ʹ substructure (Aʹ) during organosolv pretreatment. Considerable amount of C2,6-H2,6 correlation in p-hydroxybenzoate (PB) units were observed for EOL-CW, EOL-BW and EOL-AS, but not for EOL-EH and EOL-LP. PB units could potentially contribute to the high zeta potential of EOL-CW, EOL-BW and EOL-AS, and give rise to the positive effect of these three lignins.