6. Lignin Extraction Using Cellulolytic Enzymes

Lignin is one of the important biopolymers in plants. Being the second most abundant after cellulose, lignin is the only aromatic polymer found in nature. The basic unit of lignin is known to be monolignols. These monolignols undergo further reactions like depolymerization, giving rise to G and H units. Structural classification of lignin is done based on the presence of G and H units and isolated for the intended applications. Much research has been undertaken to determine the native form of lignin, but it has been difficult due to its close association with the carbohydrates in the plant cell wall. Various physicochemical methods are used to isolate lignin, which includes precipitation of acids, hydrolysis methods, and alkali pretreatments. Recent advancements have been made in lignin isolation, where methods like ultrasonication hydrothermal pretreatment are widely used. Classification of lignin involves various categories where extraction modes of classification pave an important category. Enzymes have been utilized for lignin extraction for an extended period. Cellulolytic enzyme lignin, as the name says, uses enzymes like cellulase for the extraction of lignin. Methods like hydrolysis enzymatic pretreatment are well known to extract the lignin effectively. This chapter focuses on the methodologies involved in the extraction of cellulolytic enzyme lignin, along with its structural features, pitfalls in the process, and their potential applications.