Characteristics of Lignin Fractions from Dilute Acid Pretreated Switchgrass and Their Effect on Cellobiohydrolase from Trichoderma longibrachiatum

Abstract

To investigate the interactions between acid pretreated grass lignin and cellobiohydrolase, three different lignin fractions were isolated from dilute acid pretreated switchgrass by (i) ethanol extraction, followed by (ii) dioxane/H2O extraction, and (iii) cellulase treatment, respectively. Structural properties of each lignin fraction were elucidated by GPC, 13C-NMR and 2D-HSQC NMR analyses. The adsorptions of cellobiohydrolase to the isolated lignin fractions were also studied by Langmuir adsorption isotherms. Ethanol-extractable lignin fraction, mainly composed of syringyl (S) and guaiacyl (G) units, had the lowest molecular weight, while dioxane/H2O-extractable lignin fraction had the lowest S/G ratio with higher content of p-coumaric acid (pCA) unit. The residual lignin fraction after enzymatic treatment had the highest S/G ratio without hydroxyphenyl (H) unit. Strong associations were found between lignin properties such as lignin composition and S/G ratio and its non-productive enzyme adsorption factors including the maximum adsorption capacity and binding strength.