Structural characterization of the stem cell wall lignin of <i>Euterpe oleracea</i>

Abstract

This paper aimed to characterize the lignin in the cell wall of Euterpe oleracea Mart. Samples from two regions of the base of the palm were acquired: outer and inner regions (OR and IR, respectively). The extraction with organic solvents and the treatment with 1% NaOH were carried out. Holocellulose, α-cellulose and lignin content were quantified, the latter also isolated by the Björkman method for the structural characterization using 1H and 13C NMR in the liquid state, as well as spectroscopic (FTIR) and chromatographic analysis. The extracted stem had 10.33% (OR) and 15.66% (IR) of the lignin. After the treatment with 1% NaOH, a reduction in these values was observed, and it was also possible to confirm this result through the decrease in the intensities of the signals referring to the functional groups linked to lignin and hemicellulose. The spectroscopic and chromatographic analyzes revealed GS-type lignin incorporated with p-hydroxybenzoic and protocatechuic acid in both samples. The main structural units present in the lignin were also observed, such as β-O-4 bond, β-O-4’ ϒ-acetyl bond, guaiacyl unit, syringyl unit and p-hydroxybenzoate.