Structural characterization of lignin from grape stalks (Vitis vinifera L.)
Prozil, S.ón.O.; Evtuguin, D.V.; Silva, A.M.S.; Lopes, L.ís.P.C.
Journal of Agricultural and Food Chemistry 62(24): 5420-5428
ISSN/ISBN: 0021-8561 PMID: 24892733 DOI: 10.1021/jf502267s
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.