Abstract
BackgroundThe presence of lignin normally affects enzymatic saccharification of lignocellulose detrimentally. However, positive effects of lignin on enzymatic hydrolysis have been recently reported. Enzyme–lignin interactions could be the key to reveal the underlying mechanism of their discrepant behaviors. In this study, to elucidate the positive effects of extractable lignin (EL) on enzymatic hydrolysis of ethanol organosolv-pretreated wood sawdust, two lignin fractions, EL and milled wood lignin (MWL), were isolated sequentially from pretreated substrates. Quartz crystal microbalance with dissipation (QCM-D) was then used to investigate the lignin aggregation effects on enzyme adsorption.ResultsWe found that both EL and MWL had a narrow molecular weight distribution. However, MWL had an obviously higher molecular weight than EL. This indicated that EL and MWL likely represent two distinct lignin fractions from ethanol organosolv-pretreated substrates. HSQC NMR analysis revealed that less β-O-4, β-β, and β-5 linkages and a higher S/G ratio was present in EL, as compared to MWL. QCM-D analysis showed that the enzyme adsorption on lignin was highly relevant to these lignin structural characteristics. An obviously lower maximum enzyme adsorption capacity was observed on EL films (152.63–168.09 ng/cm2) compared to MWL films (196.71–224.73 ng/cm2). Furthermore, enzyme desorption on lignin films was determined. A significantly lower irreversible enzyme adsorption was observed on EL (75.40 ng/cm2) compared to MWL (137.35 ng/cm2). More importantly, two reconstructed lignin films were designed to investigate lignin assembly on enzyme adsorption. The results indicated that the presence of EL reduced irreversible enzyme adsorption on the reconstructed lignin films by 39.2–45.0%.ConclusionsLignin structure determined the interaction between enzyme and lignins. A positive correlation was observed between molecular weight, the content of β-5 linkages, and enzyme adsorption on lignin. EL, which was more depolymerized and less condensed, had the lower enzyme adsorption of the two preparations tested. Additionally, the presence of EL reduced enzyme adsorption on reconstructed lignin films, perhaps through a mechanism involving the blocking of non-productive enzyme binding sites on the MWL. This could be the mechanism for the positive effects of EL on enzymatic hydrolysis.
Highlights
The presence of lignin normally affects enzymatic saccharification of lignocellulose detrimentally
In a typical biorefinery process, fermentable sugars are released from the biomass via enzymatic hydrolysis, and the resultant sugars are fermented to valuable products [3,4,5]
Our findings showed that both extractable lignin (EL) preparations had a lower content of aliphatic hydroxyl groups compared to milled wood lignin (MWL) lignins
Summary
The presence of lignin normally affects enzymatic saccharification of lignocellulose detrimentally. Extensive efforts have been devoted to investigate the factors affecting enzymatic hydrolysis, such as inhibition from lignin, pseudo-lignin, or hemicellulose, cellulose accessibility, non-synergistic enzyme action, etc[7,8,9,10,11,12]. Among these influential factors, the inhibitory effects of lignin on enzymatic hydrolysis have been investigated extensively. Part of lignin will still remain in pretreated substrates despite pretreatment, resulting in the enzyme non-productive binding [14]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
