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accessible for enzymatic digestion ( Grabber et al., 2008; Ralph, 2010 ). One of
the most interesting lignin redesign concepts is the attempt to generate a
lignin polymer with predesigned cleavage sites, amenable to facile chemical
degradation, based on the incorporation of coniferyl ferulate (or more gen-
erally monolignol ferulates or sinapates in angiosperms) into the lignin
polymer ( Fig. 9 ). Coniferyl ferulate represents an acylated form of coniferyl
alcohol, the main lignin constituent in conifer lignin. In vitro polymerisation
studies using peroxidases provided experimental evidence that it is possible
to generate a lignin polymer derived from coniferyl alcohol and coniferyl
ferulate ( Grabber et al., 2008 ). Ferulate behaved like a normal monolignol in
this process and participated in the lignification process by copolymerising
with the lignin polymer in the usual combinatorial manner ( Ralph, 2010 ).
The newly formed lignin polymer contained ester linkages that could easily
be hydrolysed chemically ( Fig. 8 ). This led to significant improvements in
processing efficiency including enhanced alkaline delignification and higher
fibre yields ( Grabber et al., 2008; Ralph, 2010 ). A biochemical survey of a
range of plant species has identified a small number of plants that produce
coniferyl ferulate naturally ( Ralph, 2010 ). Isolation of the gene responsible
Fig. 9. Simplified model showing one possible structure for the incorporation of
coniferyl ferulate (bold) into conifer lignin. The position of the cleavable ester linkage
is highlighted.
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