Recent advancement in lignin biorefinery: With special focus on enzymatic degradation and valorization

With the intensive development of lignocellulosic biorefineries to produce fuels and chemicals from biomassderived carbohydrates, lignin was generated at a large quantity every year. Therefore, lignin has received increasing attention as an abundant aromatics resource in terms of research and development efforts for valueadded chemicals production. In this review, studies about lignin degradation especially the crucial enzymes involved and the reaction mechanism were substantially discussed, which provided the molecular basis of lignin biodegradation. Then, the latest improvements in lignin valorization by biological methods were summarized and case studies about value-added compounds from lignin were introduced. Afterwards, challenges, opportunities and prospects regarding biorefinery of lignin were presented.