Enhancing the solubility and antioxidant activity of high-molecular-weight lignin by moderate depolymerization via in situ ethanol/acid catalysis

By Liangliang An, Chen Si, Guanhua Wang, Wenjie Sui, Zhengyi Tao. Industrial crops and products (Print), 2019

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Abstract Lignin, a by-product obtained from the pulping industry and cellulosic ethanol production, has received considerable attention for its antioxidant activity owing to its polyphenol structure. In this work, high-molecular-weight lignin obtained by ethanol-water fractionation of enzymatic hydrolysis lignin, was moderately depolymerized via in situ ethanol/acid catalysis to improve its solubility and antioxidant activity. The depolymerized products showed significant reduction in molecular weight and improvement in solubility in an 80% ethanol-water (v/v) solution owing to the cleavage of ether linkages; this was confirmed by gel permeation chromatography (GPC), fourier transform-infrared spectroscopy (FT-IR), pyrolysis-gas chromatography/ mass spectrometer (Py-GC/MS), carbon-13 nuclear magnetic resonance spectrometry (13C NMR), and heteronculear single quantum coherence nuclear magnetic resonance spectrometry (HSQC NMR) analyses. In addition, the total phenolics content of the depolymerized products increased sharply, leading to a significant enhancement in the free radical scavenging capacity of 1,1-diphenyl-2-picrylhydrazyl (DPPH). In particular, D-200 (depolymerized product at 200 °C) with IC50 = 66.0 ± 2.6 μg/mL was comparable to the positive control butylated hydroxytoluene (BHT) with IC50 = 53.3 ± 4.5 μg/mL, indicating the potential application of lignin as a high-value-added antioxidant. In conclusion, the depolymerization of high-molecular-weight lignin via moderate ethanol/acid catalysis may effectively improve its solubility and antioxidant activity.

Subfields: Biomedical Engineering, Biotechnology, Food Science

View Paper: https://www.semanticscholar.org/paper/7aff70094b300ee3e6f945578b663a71d5627227