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Table 4 Semiquantitative 2D-NMR analysis (abundances of lignin units, p-hydroxycinnamates, and carbohydrates, as per total lignin and carbohydrate units, and abundance of main lignin inter-unit linkages and end-groups, as per 100 lignin units) of the untreated and AS-CTM pretreated sugarcane bagasse samples

From: Fate of p-hydroxycinnamates and structural characteristics of residual hemicelluloses and lignin during alkaline-sulfite chemithermomechanical pretreatment of sugarcane bagasse

  Untreated 2.5% Na2SO3 + 1.25% NaOH 5% Na2SO3 + 2.5 NaOH 10% Na2SO3 + 5% NaOH RES-sap
Sample compositiona
 p-Hydroxyphenyl lignin units (H) 0.6 0.4 0.4 0.1 0.6
 Guaiacyl lignin units (G) 8.7 6.5 6.5 2.2 15.6
 Syringyl lignin units (S) 10.1 8.1 7.5 2.3 13.4
 S/G ratios 1.2 1.2 1.2 1.0 0.9
 Total lignin units 19.4 15.0 14.4 4.6 ne
 Total carbohydrate units 80.6 85.0 85.6 95.1 ne
 p-Coumarates (pCA) 10.4 10.0 9.0 1.7 2.5c
 Ferulates (FA) 4.6 3.1 1.9 0.0 0.0
Main lignin inter-unit linkages and end-groupsb
 β-O-4 Alkyl-aryl ethers (A) 60 59 49 42 4
 Phenylcoumarans (B) 5 4 4 4 4
 Cinnamyl alcohol end-groups (I) 3 3 3 0 2
  1. The data for the residual solids that remained after enzymatic hydrolysis of the sugarcane bagasse sample pretreated with 10% Na2SO3 + 5% NaOH, and after extensive saponification (1 M NaOH, 48 h, 90 °C) (RES-sap) are also shown
  2. ne not evaluated
  3. aSample composition represents the abundance of lignin units (H, G, S) and p-hydroxycinnamates (pCA, FA) from integration of their respective signals, and carbohydrate units (xylose, glucose and 4-O methyl-α-d-glucuronic acid) from integration of the anomeric carbon signals, and are referred to the total lignin (H + G + S) and carbohydrate units (lignin + carbohydrate units = 100)
  4. bThe abundance of lignin linkages (A, B) and end-groups (I) is obtained from the integration of aliphatic signals and is referred to the total lignin units (H + G + S = 100)
  5. cThese represent the pCA that bear a free carboxylic group and are etherified at the 4-OH position to either lignin or carbohydrates