Evaluating Lignin-Rich Residues from Biochemical Ethanol Production of Wheat Straw and Olive Tree Pruning by FTIR and 2D-NMR

Figure 3

Main lignin and carbohydrate structures identified in the lignin-rich residues from wheat straw and olive tree pruning WIS fractions: A, β-O-4′; B, resinols with β-β′, α-O-γ′, andγ-O-α′ linkages; C, phenylcoumarans with α-O-4′ and β-5′ linkages; D, spirodienones with β-1′, α-O-4′ linkages; FA, ferulic acid; G, guaiacyl unit; H, p-hydroxyphenyl unit; PCA, p-coumaric acid; S, syringyl unit; S′, oxidized syringyl units with a ketone; T, tricin end unit; X, xylopyranose (R, OH).