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

Table 3

Structural characteristic of lignin (main interunit linkages, aromatic units, S/G ratio, p-hydroxycinnamate content, and p-coumarate/ferulate ratio) from integration of ¹³C–¹H correlation peaks in the HSQC spectra of the fermentation residues from wheat straw and olive tree pruning WIS fractions.

	Wheat straw	Olive tree pruning
Lignin interunit linkages
β-O-4′ (A)	50	65
Resinols (B)	15	25
Phenylcoumarans (C)	32	10
Spirodienones (D)	3	—
Lignin aromatic units
H	3	1
G	60	16
S	37	83
S/G ratio	0.6	5.2
p-Hydroxycinnamates
p-Coumarates (PCA)	4.3	—
Ferulates (FA)	2.7	—
PCA/FA ratio	1.6	—