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Table 2 Semi-quantitative HSQC NMR structural characterization of residual lignin in control and fungal-treated wheat straw after 7 weeks of growth

From: Mechanistic insight in the selective delignification of wheat straw by three white-rot fungal species through quantitative 13C-IS py-GC–MS and whole cell wall HSQC NMR

  Control Cs1 Cs12 Pe3 Pe6 Le8 Le10
Lignin subunits (%)a
 H 2 (6) 3 (5) 3 (6) 3 (6) 2 (6) 2 (5) 3 (5)
 G 52 (53) 47 (49) 42 (46) 57 (57) 53 (53) 53 (54) 57 (56)
 Gox 2 (1) 11 (8) 12 (9) 2 (2) 3 (3) 6 (5) 4 (3)
 Gmod 0 (0) 3 (2) 4 (3) 0 (0) 1 (1) 0 (0) 0 (0)
 S 37 (34) 25 (26) 25 (26) 31 (30) 32 (31) 30 (29) 29 (30)
 Sox 5 (4) 10 (7) 12 (9) 6 (5) 6 (5) 6 (5) 5 (4)
 Smod 2 (1) 3 (2) 2 (2) 1 (1) 1 (1) 2 (2) 1 (1)
  S/G 0.81 (0.72) 0.62 (0.60) 0.67 (0.64) 0.65 (0.59) 0.69 (0.64) 0.63 (0.60) 0.58 (0.59)
Hydroxycinnamates (%)b
 p-Coumarate 6 (5) 5 (3) 5 (3) 5 (4) 5 (4) 5 (3) 4 (3)
 Ferulate 21 (15) 19 (14) 18 (13) 15 (12) 15 (12) 16 (13) 17 (13)
Lignan (%)b        
 Tricin 10 (7) 11 (8) 9 (7) 6 (5) 7 (5) 8 (6) 10 (8)
Lignin inter-unit linkages (%)c
 β-O-4′ Aryl ethers 43 (90) 37 (93) 32 (97) 39 (90) 39 (85) 40 (86) 40 (88)
 Phenylcoumarans 3 (6) 2 (4) 1 (2) 3 (7) 5 (11) 4 (10) 3 (7)
 Resinols 1 (3) 1 (3) 0 (1) 1 (3) 2 (4) 2 (4) 2 (4)
 Total 48 (100) 40 (100) 33 (100) 43 (100) 46 (100) 46 (100) 45 (100)
  1. Volume integration of cross peaks in the aliphatic region likely suffered from overlap with carbohydrates, especially after extensive delignification
  2. Cs  Ceriporiopsis subvermispora, Pe  Pleurotus eryngii, Le  Lentinula edodes
  3. aPercentage of subunits (H +G  +Gox + Gmod + S + Sox + Smod = 100) and in parenthesis (subunits + pCA(H) + FA(G) + T(S) = 100)
  4. bPercentage vs aromatic units and subunits + pCA + FA + T (see subscript a)
  5. cPercentage of inter-unit linkages vs total subunits and in parenthesis as percentage of total inter-unit linkages