Lignin-carbohydrate complexes (LCCs) and its role in biorefinery

Although lignocellulosic biomass is traditionally considered to be composed of cellulose, hemicellulose, and lignin, each of these components does not exist individually. Structurally, they are chemically bonded to form lignin-carbohydrate complexes (LCC) instead of being simply physically attached. Thus, lignin-carbohydrate complexes actually define the original structure of lignocellulosic biomass and inherit a wide array of compositions and features. However, the role of lignin-carbohydrate complexes has neither been completely investigated nor understood in this respect. In this review, the basic structures of lignin-carbohydrate complexes, extraction methods, bonding patterns and their cleavage are briefly discussed. More efforts are put on the role of lignin-carbohydrate complexes in the extraction/isolation of biopolymers and in the subsequent lignocellulosic biorefining processes. Finally, several design strategies for biomass pretreatment, biopolymer isolation, enzymatic hydrolysis etc. are proposed, and future research needs for industrial application of lignocellulosic biorefinery are explored. It is anticipated this review could provide both the fundamentals of LCC and its effect on the biomass utilization, in the meantime attract more scientists’ attention on the basic research on LCC.