Pretreatment with laccase and a phenolic mediator degrades lignin and enhances saccharification of Eucalyptus feedstock

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
C_α-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 C_α-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.

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