Lignin glycoside bonds

So-called accessory enzymes are also required for hydrolysis of hemicellulose in native plant tissue. These enzymes include a variety of acetyl xylan esterases (EC 3.1.1.72), acetyl esterases (EC 3.1.1.6), and esterases, such as feruloyl acid esterase (EC 3.1.1.73),178 that hydrolyze lignin glycoside bonds. They also include classes for cleavage of specific hemicellulose side chains, such as a-L-arabinofuranose, glucuronic acid, and 4-O-methyl-glucuronic acid groups. 

Such processes are always accompanied by a DP loss, either by electrophilic attack of ozone, by an ozone-catalyzed cleavage of the glycosidic bond or by attack of secondary radical species [15]. Residual lignin also plays a crucial role in ozone bleaching. Model studies showed that lignin with free phenolic hydroxyl groups accelerated carbohydrate oxidation, probably by activation of oxygen via phenoxyl radicals, whereas etherified phenolic model compounds had a protective effect [16,17]. 

JP Joseleau, R Kesraoui. Glycosidic bonds between lignin and carbohydrates. Holzforschung 40 163-16S, 1986. 

Sodium hydroxide pulp is obtained by boiling wood with 8% caustic soda under pressure at 150-170°C. By this process, the glycosidic bonds of the lignin are destroyed and lignin phenolate is formed. The sodium lignin phenolate subsequently diffuses out of the wood. 

Polysaccharides are carbohydrate polymers, formed from either mono- or disaccharides through glycosidic bonds. The most significant polysaccharides of relevance here are cellulose, starch, lignin, pectin and chitin. The structures of some of these polymers are shown in Figure 7.2. 

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