Table 4.
Lignin units and side-chains forming different inter-unit linkages from the heteronuclear single quantum correlation spectra of treated eucalypt wood and controls
| Wood | Control | Laccase only | Laccase and methyl syringate | |
|---|---|---|---|---|
|
Lignin units
| ||||
| Syringyl (S) (% total) |
78 |
79 |
86 |
100 |
| Guaiacyl (G) (% total) |
22 |
21 |
14 |
0 |
| Cα-oxidized S units (Sʹ) (% S) |
13 |
11 |
16 |
47 |
| S/G ratio |
3.6 |
3.8 |
6.3 |
- |
|
Chains forming inter-unit linkages
(% S + G) | ||||
| β-O-4ʹ Alkyl-aryl ethers (A) |
61 (86) |
48 (92) |
42 (100) |
23 (100) |
| Phenylcoumarans (B) |
0 |
0 |
0 |
0 |
| Resinols (C) |
10 (14) |
4 (8) |
0 |
0 |
| Spirodienones (D) |
0 |
0 |
0 |
0 |
| Total | 71 (100) | 52 (100) | 42 (100) | 23 (100) |
The lignin composition (S and G units), the amount of Cα-oxidized S units (with respect to total S units), the S/G ratio, and the abundance of side chains forming different inter-unit linkages (A-D) per 100 phenylpropane units were determined from the heteronuclear single quantum spectra of eucalypt wood treated with laccase (50 U · g-1) and 3% methyl syringate and laccase alone, compared with a control without enzyme and the initial wood. The percentage of side chains forming each linkage type (or end-group) are also indicated in parentheses.