College of Chemistry and Chemical Engineering, Jishou University, Jishou, China.
Key Laboratory of Hunan Forest Products and Chemical Industry Engineering, National and Local United Engineering Laboratory of Integrative Utilization of Eucommia ulmoides, Jishou University, Zhangjiajie, China.
Phytochem Anal. 2024 Jun;35(4):786-798. doi: 10.1002/pca.3328. Epub 2024 Jan 26.
Lignin has great potential as the most abundant renewable phenolic polymer. Studies have shown that lignin structure varies depending on different sources and different extraction methods. However, there are few studies on lignin in kudzu root residue.
The aim of the study was to explore optimal extraction conditions of Pueraria lobata residue lignin (PLL) with deep eutectic solvents (DESs) and characterise the structure and morphology of PLL.
Firstly, the chemical composition of kudzu root residue was determined by the Van-soest method. Then, betaine was used as hydrogen bond acceptor (HBA), nine kinds of common acids and alcohol were selected as hydrogen bond donor (HBD) to synthesise a DES to extract lignin from kudzu root residue. The influence of conditions on the extraction of PLL was explored by a betaine-based DES according to a single-factor experiment, and then the best process of PLL extraction was determined by an orthogonal experiment. Finally, the morphology and structure of PLL were analysed by scanning electron microscope (SEM), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and NMR.
Cellulose, hemicellulose, lignin, and ash content in kudzu root residue were 41.13%, 16.39%, 25.03%, and 0.41%, respectively. When the DES consisted of betaine and formic acid, the solid-liquid ratio was 1:45, the extraction time was 5.5 h at 160°C, the extraction yield of lignin was 89.29%, and the purity was 83.01%. PLL was composed of interconnected spherical particles with good thermal stability and narrow polydispersity index (PDI) distribution. FTIR and 2D-heteronuclear singular quantum correlation (HSQC) NMR illustrated that PLL was a typical G-type and S-type lignin.
This study would fill the gap of research on lignin in kudzu root residue and provide a theoretical reference for the utilisation of lignin in kudzu roots as well as a new thinking for the recycling of kudzu root resources.
木质素作为最丰富的可再生酚类聚合物具有巨大的潜力。研究表明，木质素结构因来源和提取方法的不同而有所差异。然而，关于葛根渣中木质素的研究较少。
本研究旨在探索用深共熔溶剂（DESs）从葛根渣中提取葛根木质素（PLL）的最佳条件，并对 PLL 的结构和形态进行表征。
首先，采用 Van-soest 法测定葛根渣的化学成分。然后，以甜菜碱为氢键供体（HBD），选择 9 种常见酸和醇为氢键受体（HBA）合成 DES 提取葛根渣中的木质素。根据单因素实验，考察条件对 PLL 提取的影响，然后通过正交实验确定 PLL 提取的最佳工艺。最后，通过扫描电子显微镜（SEM）、热重分析（TGA）、凝胶渗透色谱（GPC）、傅里叶变换红外光谱（FTIR）和核磁共振（NMR）对 PLL 的形态和结构进行分析。
葛根渣中纤维素、半纤维素、木质素和灰分的含量分别为 41.13%、16.39%、25.03%和 0.41%。当 DES 由甜菜碱和甲酸组成，固液比为 1:45，提取时间为 5.5 h，提取温度为 160°C 时，木质素的提取率为 89.29%，纯度为 83.01%。PLL 由相互连接的球形颗粒组成，具有良好的热稳定性和较窄的多分散指数（PDI）分布。FTIR 和二维异核单量子相关（HSQC）NMR 表明，PLL 是一种典型的 G 型和 S 型木质素。
本研究将填补葛根渣中木质素研究的空白，为葛根木质素的利用以及葛根资源的循环利用提供理论参考。
