resumo
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.
palavras-chave
CHEMICAL-COMPOSITION; MACROMOLECULAR COMPONENTS; HIBISCUS-CANNABINUS; WOOD; FEATURES; WASTE; PORTUGAL; HARDWOOD; POMACE; WINERY
categoria
Agriculture; Chemistry; Food Science & Technology
autores
Prozil, SO; Evtuguin, DV; Silva, AMS; Lopes, LPC
nossos autores
Dmitry Evtyugin
Professor Associado com Agregação
Sónia Oliveira Prozil
Bolseiro de investigaçãoagradecimentos
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.