Efficiently producing second-generation biofuels from biomass is of strategic significance and meets sustainability targets, but it remains a long-term challenge due to the existence of biomass recalcitrance. Lignin contributes significantly to biomass recalcitrance by physically limiting the access of enzymes to carbohydrates, and this could be partially overcome by applying a pretreatment step to directly target lignin. However, lignin typically cannot be completely removed, and its structure is also significantly altered during the pretreatment. As a result, lignin residue in the pretreated materials still significantly hindered a complete conversion of carbohydrate to its monosugars by interacting with cellulase enzymes. The non-productive adsorption driven by hydrophobic, electrostatic, and/or hydrogen bonding interactions is widely considered as the major mechanism of action governing the unfavored lignin-enzyme interaction. One could argue this type of interaction between lignin residue and the activated enzymes is the major roadblock for efficient enzymatic hydrolysis of pretreated lignocellulosics. To alleviate the negative effects of lignin on enzyme performance, a deep understanding of lignin structural transformation upon different types of pretreatments as well as how and where does lignin bind to enzymes are prerequisites. In the last decade, the progress toward a fundamental understanding of lignin-enzyme interaction, structural characterization of lignin during pretreatment and/or conformation change of enzyme during hydrolysis is resulting in advances in the development of methodologies to mitigate the negative effect of lignin. Here in this review, the lignin structural transformation upon different types of pretreatments and the inhibition mechanism of lignin in the bioconversion of lignocellulose to bioethanol are summarized. Some technologies to minimize the adverse impact of lignin on the enzymatic hydrolysis, including chemical modification of lignin, adding blocking additives, and post-treatment to remove lignin were also introduced. The production of liquid biofuels from lignocellulosic biomass has shown great environmental benefits such as reducing greenhouse gas emissions and mitigate climate change. By addressing the root causes of lignin-enzyme interaction and how to retard this interaction, it is our hope that this comprehensive review will pave the way for significantly reducing the high cost associated with the enzymatic hydrolysis process, and ultimately achieving a cost-effective and sustainable biorefinery system.

从生物质中高效生产第二代生物燃料具有战略意义并符合可持续发展目标，但由于生物质不适应的存在，这仍然是一项长期挑战。木质素通过物理限制酶对碳水化合物的访问而显着导致生物质顽固，这可以通过应用预处理步骤直接靶向木质素来部分克服。然而，木质素通常不能完全去除，并且在预处理过程中其结构也会发生显着改变。结果，预处理材料中的木质素残留物仍然通过与纤维素酶相互作用显着阻碍碳水化合物向其单糖的完全转化。由疏水、静电、和/或氢键相互作用被广泛认为是控制不利的木质素-酶相互作用的主要作用机制。有人可能会争辩说，木质素残基和活化酶之间的这种相互作用是预处理木质纤维素有效酶水解的主要障碍。为了减轻木质素对酶性能的负面影响，深入了解不同类型预处理后的木质素结构转变以及木质素如何以及在何处与酶结合是先决条件。在过去的十年中，对木质素-酶相互作用的基本理解取得了进展，预处理过程中木质素的结构表征和/或水解过程中酶的构象变化导致了减轻木质素负面影响的方法的发展。在这篇综述中，总结了不同类型预处理后的木质素结构转变以及木质素在木质纤维素生物转化为生物乙醇中的抑制机制。还介绍了一些减少木质素对酶水解不利影响的技术，包括木质素的化学改性、添加封闭添加剂和去除木质素的后处理。从木质纤维素生物质生产液体生物燃料已显示出巨大的环境效益，例如减少温室气体排放和减缓气候变化。