Beijing Key Laboratory of Bioprocess, College of Life Science and Technology, Beijing University of Chemical Technology, Beijing 100029, China.
Beijing Zest Bridge Media Technology Inc., Beijing 100176, China.
Molecules. 2022 May 2;27(9):2905. doi: 10.3390/molecules27092905.
The formosolv fractionation process has been demonstrated to be an effective approach toward lignin recovery as an antioxidant from lignocellulosic biomass. In this study, four lignin fractions, FL-88%, FSL-70%, FIL-70% and FL-EtAc, were isolated from biomass through two-step formosolv fractionation (88% formic acid delignification followed by 70% aqueous formic acid fractionation). To better understand the structural properties of the lignin obtained from this fractionation process, four isolated lignins were successfully characterized by gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance (2D-HSQC NMR) spectroscopy, thermogravimetric analysis (TGA) and gas chromatograph-mass spectroscopy (GC/MS). It was found that lignin depolymerization via β--4 cleavage occurred via a formylation, elimination and hydrolysis mechanism, accompanied by a competitive condensation reaction. Noteworthily, two-step formosolv fractionation can produce specific lignin fractions with different ABTS and DPPH radical scavenging activities. The FL-EtAc fraction with low molecular weight (M = 2748 Da) and good homogeneity (PDI = 1.5) showed excellent antioxidant activity, compared with the other three isolated lignin fractions, even equal to that of commercial antioxidant BHT at the same concentration of 2.0 mg·mL. These findings are of great help for specific lignin from biomass as a natural antioxidant in the future.
Formosolv 分级法已被证明是从木质纤维素生物质中回收木质素作为抗氧化剂的有效方法。在这项研究中，通过两步 formosolv 分级法（88%甲酸脱木质素，然后进行 70%甲酸水溶液分级），从生物质中分离出四种木质素级分，即 FL-88%、FSL-70%、FIL-70%和 FL-EtAc。为了更好地了解从该分级过程中获得的木质素的结构特性，通过凝胶渗透色谱（GPC）、傅里叶变换红外（FT-IR）、二维异核单量子相干核磁共振（2D-HSQC NMR）光谱、热重分析（TGA）和气相色谱-质谱（GC/MS）成功地对四种分离出的木质素进行了表征。结果表明，木质素通过β-O-4 键的断裂发生甲酰化、消除和水解反应，同时伴有竞争性缩合反应。值得注意的是，两步 formosolv 分级法可以产生具有不同 ABTS 和 DPPH 自由基清除活性的特定木质素级分。与其他三种分离的木质素级分相比，具有低分子量（M = 2748 Da）和良好均一性（PDI = 1.5）的 FL-EtAc 级分表现出优异的抗氧化活性，甚至在相同浓度为 2.0 mg·mL 时，其抗氧化活性与商业抗氧化剂 BHT 相当。这些发现对未来将生物质中的特定木质素作为天然抗氧化剂具有重要意义。
