Biomass lignin is an important factor in enzymatic hydrolysis and sugar yields. Several mechanisms have been suggested about how lignin limits enzymatic hydrolysis:
1. toxic to the enzymes for simple phenolic compounds
2. steric hindrance caused by lignin-polysaccharide linkages that limit access of fibrolytic enzymes to specific carbohydrate moieties. For example, the degradation rate of xylan is said to depend on the number and location of side branches and their lignin associations
3. Lignin as hydrophobic filler that displaces water in the cell wall matrix. As a result of the hydrophobicity of lignin, water cannot enter internal polymers of the cell wall. Hence, the action of hydrophilic enzymes may be limited by this hydrophobic environment
4. Adsorption of enzymes, which increases the loading but decreases the effects
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