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 H-1 and C-13 NMR spectroscopy and PO indicates the predominance of beta-O-4' structures (39% mol) in grape stalk lignin together with moderate amounts of beta-5', beta-beta, beta-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.
keywords
CHEMICAL-COMPOSITION; MACROMOLECULAR COMPONENTS; HIBISCUS-CANNABINUS; WOOD; FEATURES; WASTE; PORTUGAL; HARDWOOD; POMACE; WINERY
subject category
Agriculture; Chemistry; Food Science & Technology
authors
Prozil, SO; Evtuguin, DV; Silva, AMS; Lopes, LPC
our authors
Dmitry Evtyugin
Associate Professor with Aggregation
Sónia Oliveira Prozil
Research Fellowshipacknowledgements
We thank the Portuguese Foundation for Science and Technology (FCT project PTDC/AGR-AAM/104911/2008) and the Operation Program of Competitive Factors (COMPETE, ref FCOMP-01-0124-FEDER-008734) for financial support of this work.