460 / 2018-09-05 10:05:39

Extractable lignin deposition enhanced enzymatic hydrolysis of ethanol organosolv pretreated wood sawdust

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The deposition of lignins was observed on the surfaces of ethanol organosolv pretreated wood sawdust, which might affect the enzymatic hydrolysis. To investigate the effects of lignin deposition, the deposited lignins were removed by ethanol washing in this study. This surprisingly led to the decline of enzymatic hydrolysis efficiency of pretreated substrates, suggesting the positive effects of the lignin deposition. To figure out the underlying mechanism, the residual lignins in ethanol organosolv pretreated substrates were fractionated into two components (extractable lignins, and bulk lignins) in this study. Extractable lignins (EL) represented as the deposited lignins, and isolated by ethanol extraction of pretreated substrates, while the milled wood lignins (MWL) were used to represent the bulk lignin, and isolated from the extractive-free pretreated substrates. The EL and MWL lignins were fully characterized by GPC, HSQC NMR, and 31P NMR analysis. The results indicated that the molecular weight of EL was much lower than MWL. Moreover the EL lignins had the less condensed structure and a higher content of carboxylic groups, compared to MWL lignins. These could be used to explain the difference on enzyme adsorption behavior on EL and MWL films determined by quartz crystal microbalance (QCM). The irreversible enzyme adsorption mass was 137.35, and 75.40 ng/m2 respectively for MWL, and EL lignin films. More interestingly, an obvious decrease on irreversible enzyme adsorption mass was observed on the MWL/EL lignin film (MWL and EL mixed in a ratio of 1:1). The presence of EL could reduce the irreversibly adsorbed enzyme by 39.18%. Therefore, the EL lignin deposition could suppress the enzyme non-productive binding on the residual bulk lignins, which resulted in the improvement on enzymatic hydrolysis. Additionally, the pretreatment with 2-naphthol intensified the EL deposition on the pretreated substrates, obviously enhancing the enzymatic hydrolysis.