title: Structural characterization of lignin from grape stalks (Vitis vinifera L.).
abstract: The chemical structure of lignin from grape stalks, an abundant waste of winemaking, has been studied. The dioxane lignin was isolated from extractive- and protein-free grape stalks (Vitis vinifera L.) by modified acidolytic procedure and submitted to a structural analysis by wet chemistry (nitrobenzene and permanganate oxidation (PO)) and spectroscopic techniques. The results obtained suggest that grape stalk lignin is an HGS type with molar proportions of p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) units of 3:71:26. Structural analysis by (1)H and (13)C NMR spectroscopy and PO indicates the predominance of β-O-4' structures (39% mol) in grape stalk lignin together with moderate amounts of β-5', β-β, β-1', 5-5', and 4-O-5' structures. NMR studies also revealed that grape lignin should be structurally associated with tannins. The condensation degree of grape stalks lignin is higher than that of conventional wood lignins and lignins from other agricultural residues.
authors.affiliation: CICECO/QOPNA and Department of Chemistry, University of Aveiro , 3810-193 Aveiro, Portugal.
authors.forename: Sónia O
authors.initials: SO
authors.lastname: Prozil
authors.forename: Dmitry V
authors.initials: DV
authors.lastname: Evtuguin
authors.forename: Artur M S
authors.initials: AM
authors.lastname: Silva
authors.forename: Luísa P C
authors.initials: LP
authors.lastname: Lopes
mesh_terms: D008031:Lignin / Q000737:chemistry* / Q000302:isolation & purification; D009682:Magnetic Resonance Spectroscopy; D017895:Manganese Compounds / Q000737:chemistry; D015394:Molecular Structure; D008970:Molecular Weight; D009578:Nitrobenzenes / Q000737:chemistry; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry; D018547:Plant Stems / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D027843:Vitis / Q000737:chemistry*
chemical_list: D017895:Manganese Compounds; D009578:Nitrobenzenes; D010087:Oxides; C048856:permanganic acid; D008031:Lignin; C036077:nitrobenzene