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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