title: Structural characterization of lignin: a potential source of antioxidants guaiacol and 4-vinylguaiacol.
abstract: The structure of lignin obtained from the ozone and soaking aqueous ammonia pretreatment of wheat straw has been characterized utilizing chemical analytical methods in order to reveal its antioxidant characteristics, including attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), pyrolysis/tetramethylammonium hydroxide-gas chromatography/mass spectrometry (Py/TMAH-GC/MS), gel permeation chromatography (GPC), ultra violet-visible spectroscopy (UV-vis), and 1,1-diphenyl-2-picrylhydrazyl (DPPH) antioxidant evaluation assay. The results demonstrated that the isolated lignin is a ρ-hydroxyphenyl- guaiacyl-syringyl (H-G-S) lignin, with S/G ratio of 0.35 and significant amounts of phenol 2-methoxy (guaiacol) and phenol 2-methoxy-4-vinyl (4-vinylguaiacol). The Py-GC/MS and Py/TMAH-GC/MS pyrograms indicated that the major units in this lignin are derived from hydroxycinnamic acids. The GPC results revealed the molecular weight of the lignin was considerably low and also the FTIR analysis showed that the lignin possessed hydroxyl and methoxy functional groups; the factors led to the extracted lignin having a comparable antioxidant activity to that of currently used commercial antioxidants. The UV-vis and DPPH antioxidant assay results suggested a percentage of inhibition of the DPPH radicals in the following order: guaiacol (103.6 ± 1.36)>butylated hydroxytoluene (103.3 ± 1)>ferulic acid (102.6 ± 0.79)>pretreated lignin (86.9 ± 0.34).
authors.affiliation: Department of Biological Systems Engineering, Washington State University, Pullman, WA 99164-6120, USA. Electronic address: mohammadali.azadfar@wsu.edu.
authors.forename: Mohammadali
authors.initials: M
authors.lastname: Azadfar
authors.affiliation: Department of Biological Systems Engineering, Washington State University, Pullman, WA 99164-6120, USA.
authors.forename: Allan Haiming
authors.initials: AH
authors.lastname: Gao
authors.affiliation: Department of Biological Systems Engineering, Washington State University, Pullman, WA 99164-6120, USA.
authors.forename: Mahesh V
authors.initials: MV
authors.lastname: Bule
authors.affiliation: Department of Biological Systems Engineering, Washington State University, Pullman, WA 99164-6120, USA. Electronic address: chens@wsu.edu.
authors.forename: Shulin
authors.initials: S
authors.lastname: Chen
mesh_terms: D000975:Antioxidants / Q000494:pharmacology*; D001713:Biphenyl Compounds / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry; D006139:Guaiacol / Q000031:analogs & derivatives* / Q000494:pharmacology*; D008031:Lignin / Q000737:chemistry*; D008970:Molecular Weight; D010851:Picrates / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D014908:Triticum / Q000737:chemistry; D014866:Waste Products
chemical_list: D000975:Antioxidants; D001713:Biphenyl Compounds; D010851:Picrates; D014866:Waste Products; D006139:Guaiacol; C014245:4-vinylguaiacol; D008031:Lignin; C004931:1,1-diphenyl-2-picrylhydrazyl
keywords: Antioxidant activity; Characterization; Hydroxycinnamic acids; Wheat straw lignin