Analysis of Native Bonds Between Lignin and Carbohydrate by Specific Chemical Reactions

Abstract

Lignin-carbohydrate complexes (LCCs) are one of the glycoconjugates in which hydrophobic lignin is chemically bound to hydrophilic polysaccharides in wood cell walls. So far, several types of lignin-carbohydrate linkages have been proposed. These include: (1) benzyl ether type (Fig. 4.1; Košíková et al. 1979; Yaku et al. 1981; Koshijima et al. 1984; Eriksson and Lindgren 1977; Watanabe et al. 1989; Ohnishi et al. 1992), in which the α-hydroxyl group of the lignin is etherified with the hydroxyl group of carbohydrate; (2) benzyl ester type (Fig. 4.2; Yaku et al. 1976; Eriksson et al. 1980; Takahashi and Koshijima 1988b; Obst 1982; Lundquist et al. 1983; Das et al. 1984; Watanabe and Koshijima 1988; Imamura et al. 1994), in which the α-hydroxyl group of the lignin is esterified with the carboxyl group of glucuronic acid residue; (3) glycoside type (Fig. 4.3: Hayashi 1961; Smelstorius 1974; Yaku et al. 1976; Joseleau and Kesraoui 1986; Kondo et al. 1990a; Ford 1990), in which alcoholic or phenolic hydroxyl groups of the lignin are glycosylated by the reducing end group of carbohydrates; and (4) acetal type, in which two hydroxyl groups of carbohydrate are linked to lignin by an acetal linkage (Fig. 4.4; Bolker and Sommerville 1963; Xie et al. 2000). Among the chemical linkages, the benzyl ether and ester types have been considered to be the most probable mode of linkage (Watanabe 1995).