By analogy with fatty acid b-oxidation, a CoA-dependent b-oxidative cleavage of feruloyl-CoA was suggested, leading to the formation of vanilloyl-CoA; this compound would then be reduced
to vanillin (presumably in a reaction analogous to that of cinnamoyl-CoA reductase in the pathway to monolignols) or alternatively deacylated to vanillic acid (Fig. 2).