abstract
The chemical composition and the structural features of macromolecular components from red grape skins (variety Touriga Nacional) have been evaluated. The results of chemical analyses revealed the following contents of the main constituents: cellulose (20.8%), hemicelluloses (12.5%), proteins (18.8%), tannins (13.8%), extractives soluble in dichloromethane (5.0%) and ash (7.8%). Cellulose of grape skins is typical cellulose I polymorph with a degree of crystallinity of 66.1% as assessed by X-ray scattering. The hemicelluloses were analyzed by neutral sugars analysis, methylation analysis and 1D/2D H-1 NMR. The water-soluble compounds (26.4%) are composed mainly of monomeric sugars (glucose and fructose) and a complex mixture of hemicelluloses, the most abundant being pectin and acetylated glucomannan. The major part of structural polysaccharides (cellulose, xylan, xyloglucan, etc.) is embedded in cuticular layer and is poorly accessible to the acid hydrolysis. The cuticular substances contributed to ca. 8.5% of grape skins and their chemical structure has been evaluated by methanolysis. The possibility of comprehensive utilization of grape skins has been discussed. (C) 2012 Elsevier B.V. All rights reserved.
keywords
VITIS-VINIFERA L.; BERRY CELL-WALLS; STRUCTURAL-CHARACTERIZATION; BY-PRODUCTS; CHEMICAL-CHARACTERIZATION; ANTIOXIDANT ACTIVITY; CONDENSED TANNINS; WOOD ADHESIVES; POLYSACCHARIDES; EXTRACTION
subject category
Agriculture
authors
Mendes, JAS; Prozil, SO; Evtuguin, DV; Lopes, LPC
our authors
Dmitry Evtyugin
Associate Professor with Aggregationacknowledgements
The Portuguese Foundation for Science and Technology-FCT (Project PTDC/AGR-AAM/104911/2008) and the Operation Program of Competitive Factors-COMPETE (FCOMP-01-0124-FEDER-008734) for financial support. The authors also wish to thank the Adega Cooperativa de Silgueiros for kindly providing the grape pomace samples.