英文----经漆酶介体体系到处理后黄麻纤维中木质素结构的影响.doc
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1、Structural changes of lignin in the jute fiber treated by laccase and mediator systemYongbing Zhang, Qiang Wang*, Xuerong Fan, Jiugang YuanKey Laboratory of Science and Technology of Eco-Textile, Ministry of Education, Jiangnan University, Wuxi, Jiangsu 214122, PR China*Corresponding author. Tel.: +
2、86-510-85912007; fax: 86-510-855912009.E-mail address: qiang_.AbstractTo study the structural changes of lignin in the jute fiber treated with laccase and mediator system (LMS), lignins from the control and LMS-treated jute fiber were isolated and characterized by gel permeation chromatography (GPC)
3、, elemental analysis, measurement of phenolic hydroxyl group content, FTIR and 1H NMR. The results showed that the molecular weights of the lignin from LMS-treated jute fiber were lower than those of the lignin from the control jute fiber. The contents of phenolic hydroxyl group, aliphatic hydroxyl
4、group and methoxy group of the lignin from LMS-treated jute fiber decreased, while the content of carboxyl group increased.Keywords: laccase, jute fiber, lignin, degradation, mediator1. IntroductionThe jute fiber lignin is composed of p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) units with a H
5、/G/S composition of 2:32:66 and a S/G ration of 2.1 1. The lignin content in jute fiber is up to ca. 16%, which resulted in the coarseness and rigidity of the fiber. Therefore, jute fibers are mainly used to make the low-grade goods such as package fabrics and bags 2-3. The removal of lignin from ju
6、te fiber is proved to be a key step in the manufacturing of high-value textile products. In the traditional process, the lignins in jute fibers are eliminated mainly in degumming using some chemical products, which often cause severe environmental pollution. In order to overcome the disadvantages of
7、 chemical degumming, enzymatic degumming has been attracted a great deal of attention.Laccases (benzenediol:oxygen oxidoreductases, EC 1.10.3.2) are a widespread group of multi-copper enzymes 4. It has been reported by many researchers that laccase can degrade or polymerize the phenolic compounds in
8、 lignin 5-6. Furthermore, when laccase is used in the presence of a mediator, such as 2,2-azonabis(3-ethylbenzthiazoline-6sulfonate) (ABTS) 6, 1-hydroxybenzotriazole (HOBT) 7 and 2,2,6,6-tetramethyl-piperidine-N-oxyl (TEMPO) 8, it can further degrade the nonphenolic subunits of lignin. The mediators
9、 have high redox potential values and can produce radicals which transfer electrons from lignin to the enzyme, which finally reduces oxygen to water 9-11. The use of a laccase-mediator system (LMS) is one of the promising possibilities as environmentally benign processes for pulp biobleaching 12-13,
10、 enzymatic pulping 14 and old newspaper deinking 15 because of its ability to delignify.Bio-degumming refers to the enzymatic removal of the non-cellulosic matters such as waxes, pectins and lignins from the surface of bast fiber, which endows the fiber with better hydrophilicity in favor of subsequ
11、ent processes. Laccase is also a promising enzyme for the degumming of bast fibers to remove lignins because of its ability of delignification. Ren et al. reported that the lignin content of linen fibers treated by laccase was decreased from 4.4% to 2.3% 16. Liu et al. investigated the degumming of
12、jute fibers with laccase and pectinase 17. They found that the complex enzyme showed better removing effect for lignin. In our previous work, the degumming of linen/cotton fabric with pectinase, cellulose, xylanase and laccase were investigated 18. The results showed that laccase treatment was the b
13、est way to remove lignins from linen/cotton fabric, but it still had a big gap compared to the traditional process. These results indicated that degumming of bast fibers with laccase is a feasible method. Nevertheless, the mechanism of lignin oxidation during bast fiber degumming with LMS is not wel
14、l established. Degumming of bast fibers with LMS may be improved if the fundamental chemical reactions contributing to this process are well understood. In this study, the jute fibers were treated by LMS, and then the lignins were extracted from it with dioxane/water solution. The structure changes
15、of lignins from the control and LMS-treated jute fibers were characterized by GPC, elemental analysis, FTIR and 1H NMR. We hope the results will provide useful references to the degumming of jute fibers with LMS.2. Materials and Methods2.1 MaterialsJute fiber was supplied by Changshu Aocun Longtai w
16、eaving Co., Ltd. Laccase from Trametes Versicolor with an activity of 5.43 U/mg was supplied by Sigma. One unit of laccase activity was defined as the amount of enzyme converting 1 mole of catechol per minute in 50 mM sodium citrate buffer (pH 6) at 25oC using catechol as substrate. 2,2-azinobis(3-e
17、thylbenzthiazoline-6-sulphonate) (ABTS) provided by Sigma was used as a mediator.2.2 Treatment of the jute fibers with LMSThe reaction solution (300 mL) contained jute fibers (13 g), laccase (total activity 160 U), ABTS (10 mg), sodium acetate buffer (0.05M, pH 6). The mixtures were shaken and bubbl
18、ed air at 25oC for 6 h. After the enzymatic reaction, the jute fibers were washed several times with water, and air-dried.2.3 Isolation of lignins from the jute fibersThe corresponding residual lignins in the control and LMS-treated jute fibers, Lc and Lt, were isolated using a method as described b
19、y Evtuguin et al. with slight modification 19.The control and LMS-treated jute fibers were ground to 40 mesh fractions, refluxed with ethanol-benzene (1:2, v/v) solvent for 6 h, and then dried at room temperature. These fractions were refluxed with dioxane-water (9:1, v/v) solution containing 0.2 M
20、HCl at 90oC for 60 min. The liquid phase was decanted after the mixture was cooled to room temperature. The solid residue was subjected to the next extraction as described above, and then decanted the liquid phase. The two portions of the liquid phases were mixed, and concentrated to around 60 mL by
21、 vacuum evaporation at 40oC. The lignins were precipitated from dioxane solution by dilution into cold water (about 800 mL). The precipitate was separated by centrifugation, followed by being washed with water and freeze-dried. The crude lignins were further purified according to the method of Lundq
22、uist et al. 20.2.4 Acetylation of lignins from the jute fibersThe Lc and Lt were acetylated using a method proposed by Jahan et al. 21. Lignin of 100 mg was added in 9 mL of pyridine-acetic anhydride solution(1:2, v/v)and kept for 72 h in dark. The solution was poured into a 10-fold volume of an ice
23、-water bath where the acetylated lignins were recovered as a precipitate, which were further purified by successive washing with water and dried under vacuum. The acetylated lignins were used for 1H NMR analysis.2.5 Estimation of molecular weightThe number-average molecular weight (Mn) and weight-av
24、erage molecular weight (Mw) of Lc and Lt were determined by GPC. The GPC equipment used was a Waters 1515 Isocratic HPLC Pump (Waters Corporation, Milford, USA), with a Waters 2414 Refractive Index Detector (Waters Corporation, Milford, USA) and a GPC KD-802 Packed Column (Shodex, Japan).The lignin
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