title: Isolation and structural characterization of the milled wood lignin, dioxane lignin, and cellulolytic lignin preparations from brewer's spent grain.
abstract: The structure of the lignin from brewer's spent grain (BSG) has been studied in detail. Three different lignin preparations, the so-called "milled-wood" lignin (MWL), dioxane lignin (DL), and cellulolytic lignin (CEL), were isolated from BSG and then thoroughly characterized by pyrolysis GC/MS, 2D-NMR, and derivatization followed by reductive cleavage (DFRC). The data indicated that BSG lignin presents a predominance of guaiacyl units (syringyl/guaiacyl ratio of 0.4-0.5) with significant amounts of associated p-coumarates and ferulates. The flavone tricin was also present in the lignin from BSG, as also occurred in other grasses. 2D-NMR (HSQC) revealed that the main substructures present are β-O-4' alkyl-aryl ethers (77-79%) followed by β-5' phenylcoumarans (11-13%) and lower amounts of β-β' resinols (5-6%) and 5-5' dibenzodioxocins (3-5%). The results from 2D-NMR (HMBC) and DFRC indicated that p-coumarates are acylating the γ-carbon of lignin side chains and are mostly involved in condensed structures. DFRC analyses also indicated a minor degree of γ-acylation with acetate groups, which takes place preferentially on S lignin (6% of S units are acetylated) over G lignin (only 1% of G units are acetylated).
authors.affiliation: Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), CSIC, P.O. Box 1052, E-41080 Seville, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Rencoret
authors.forename: Pepijn
authors.initials: P
authors.lastname: Prinsen
authors.forename: Ana
authors.initials: A
authors.lastname: Gutiérrez
authors.forename: Ángel T
authors.initials: ÁT
authors.lastname: Martínez
authors.forename: José C
authors.initials: JC
authors.lastname: Del Río
mesh_terms: D000215:Acylation; D055162:Biocatalysis; D002480:Cellulase / Q000737:chemistry; D004146:Dioxanes / Q000737:chemistry / Q000302:isolation & purification; D002523:Edible Grain / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D008031:Lignin / Q000737:chemistry* / Q000302:isolation & purification*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010936:Plant Extracts / Q000737:chemistry* / Q000302:isolation & purification*; D014866:Waste Products / Q000032:analysis*; D014934:Wood / Q000737:chemistry*
chemical_list: D004146:Dioxanes; D010936:Plant Extracts; D014866:Waste Products; D008031:Lignin; D002480:Cellulase; C025223:1,4-dioxane
keywords: DFRC; HSQC; Py-GC/MS; TMAH; brewer’s spent grain; lignin