Abstract
Xylose residue (XR), after diluted acid treatment of corncob, consists of cellulose and lignin. However, structural changes of XR lignin have not been investigated comprehensively, and this has seriously hindered the efficient utilization of lignin. In this study, corncob milled wood lignin (CC MWL), and xylose residue milled wood lignin (XR MWL) were isolated according to the modified milled wood lignin (MWL) method. The structural features of two lignin fractions were thoroughly investigated via fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and two dimensional nuclear magnetic resonance (2D NMR) spectroscopy techniques. XR MWL with higher yield and lower bound carbohydrate contents presented more phenolic OH contents than CC MWL due to partial cleavage of β-O-4. Furthermore, the molecular weights of XR MWL were increased, possibly because of condensation of the lignin during the xylose production. A study on antioxidant activity showed that XR lignin had better radical scavenging ability than that of 2,6-Di-tert-butyl-4-methyl-phenol (BHT) and CC MWL. The results suggested that the lignin in xylose residue, showing great antioxidant properties, has potential applications in food additives.
Highlights
Efficient exploitation of lignocellulose for producing bio-fuels, bio-chemicals, and bio-materials can decrease the consumption of fossil fuels [1]
The lignin relative contents in xylose residue increased to 23.1 wt%
The decrease of xylose content in Xylose residue (XR) milled wood lignin (MWL) suggested that the ether bonds between xylan and lignin were cleaved after diluted acid pretreatment [16]
Summary
Efficient exploitation of lignocellulose for producing bio-fuels, bio-chemicals, and bio-materials can decrease the consumption of fossil fuels [1]. With the aim to reveal the hindrance of residual lignin during the subsequent enzymatic hydrolysis/fermentation, it is necessary to investigate the structural variation of lignin during the production of xylose. The efficient utilization of lignin in XR was another approach to improve the economic benefits of xylose and bioethanol [6,7]. It is essential that the comparative characterizations of the lignin in the corncob biorefineries, prior to utilization of lignin for chemicals and materials, facilitated the further development of bio-chemicals and bio-materials production. Comparative characterizations of lignin form reaction stages in the corncob biorefinery will facilitate more effective deconstruction of lignocellulose, and enable faster development of bio-fuel, bio-chemicals, and bio-materials production from byproduct lignin
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