Naturally p -Hydroxybenzoylated Lignins in Palms

The industrial production of palm oil concurrently generates a substantial amount of empty fruit bunch (EFB) fibers that could be used as a feedstock in a lignocellulose-based biorefinery. Lignin byproducts generated by this process may offer opportunities for the isolation of value-added products, such as p -hydroxybenzoate ( p Bz), to help offset operating costs. Analysis of the EFB lignin by nuclear magnetic resonance (NMR) spectroscopy clearly revealed the presence of bound acetate and p Bz, with saponification revealing that 1.1 wt% of the EFB was p Bz; with a lignin content of 22.7 %, 4.8 % of the lignin is p Bz that can be obtained as a pure component for use as a chemical feedstock. Analysis of EFB lignin by NMR and derivatization followed by reductive cleavage (DFRC) showed that p Bz selectively acylates the γ-hydroxyl group of S units. This selectivity suggests that p Bz, analogously with acetate in kenaf, p -coumarate in grasses, and ferulate in a transgenic poplar augmented with a feruloyl-CoA monolignol transferase (FMT), is incorporated into the growing lignin chain via its γ- p -hydroxybenzoylated monolignol conjugate. Involvement of such conjugates in palm lignification is proven by the observation of novel p -hydroxybenzoylated non-resinol β–β-coupled units in the lignins. Together, the data implicate the existence of p -hydroxybenzoyl-CoA:monolignol transferases that are involved in lignification in the various willows ( Salix spp.), poplars and aspen ( Populus spp., family Salicaceae), and palms (family Arecaceae) that have p -hydroxybenzoylated lignins. Even without enhancing the levels by breeding or genetic engineering, current palm oil EFB ‘wastes’ should be able to generate a sizeable stream of p -hydroxybenzoic acid that offers opportunities for the development of value-added products derived from the oil palm industry.