Full text
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| Author(s): |
Ana Maria dos Santos Camargos
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Lorena. |
| Institution: | Universidade de São Paulo (USP). Ciência e Engenharia dos Materiais (IFS/EES) |
| Defense date: | 2020-05-15 |
| Examining board members: |
André Luis Ferraz;
Sarita Cândida Rabelo
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| Advisor: | André Luis Ferraz |
| Abstract | |
Lignocellulosic material utilization in biorefineries, such as sugarcane bagasse, meets the current demand for more sustainable technologies. In this context, xylan, the most abundant hemicellulosic polysaccharide in grasses, has the potential for several biotechnological applications in industry. This polysaccharide has physical and chemical interactions with other cell wall components, requiring one or more pre-treatment steps to increase polysaccharides accessibility for their utilization. Among the most employed treatments, alkaline-sulfite chemothermomechanical process is responsible for lignin fractions solubilization and low polysaccharide removal. The pretreated solids can be forwarded to enzymatic saccharification and fermentation. However, pentoses fermentation is not as efficient as that of hexoses, demonstrating that it would be interesting to isolate the xylan fraction, generating new value-added products. This extraction can be carried out through enzymatic treatment, however the extracted xylans have a low molar mass. In addition, they are possibly associated with hydroxycinnamic acids through an ester bond between arabinose and hydroxycinnamic acid. Low molar mass xylans cross-linking from the phenolic terminals of hydroxycinnamic acids catalyzed by oxidative enzymes is an alternative to increase the molecular size and enable the applications of these polymeric materials. Thus, the present work evaluated xylan extraction from alkaline-sulfite pretreated sugarcane bagasse using xylanases and developed enzymatic cross-linking processes of the xylan fractions using oxidative enzymes such as horseradish peroxidase (HRP) and laccase. The chemical characterization of xylan extracted with endoxylanases showed that it contained about 1% of ferulic acid and 4% of p-coumaric acid, which represent possible oxidative coupling sites in the material. The laccase-catalyzed oxidative coupling of this xylan was developed based on a 22 experimental design, in which it was verified that only the enzymatic load significantly affected the formation of a cross-linked xylan, while the reaction time between 4 h and 24 h did not affect the reaction. The chemical and spectroscopic characterization of a cross-linked xylan prepared after reaction scale-up revealed a material composed of xylan, but also proteins which precipitated during the xylan recovery process. The cross-linked xylan molar mass was about 90 times higher than that of originally extracted xylan. The UV spectra of the starting xylan and the cross-linked xylan differed in the characteristic absorptions of the hydroxycinnamic conjugated structures, suggesting that the oxidative coupling occurred due to the precursors α-β unsaturation opening. The extracted and cross-linked xylans also exhibited antioxidant activity against the ABTS radical. The oxidative coupling assays using two HRPs demonstrated that, even to a smaller extent, xylans of higher molar mass were observed at the highest enzyme load tested. In general, the work indicated that it is possible to crosslink xylan from sugarcane bagasse through an oxidative enzymatic route and, thus, generate new materials that can add value to the use of sugarcane bagasse in the context of biorefineries. (AU) | |
| FAPESP's process: | 18/17417-5 - Low molar mass xylans polymerization via hydroxycinnamic acids oxidative coupling |
| Grantee: | Ana Maria dos Santos Camargos |
| Support Opportunities: | Scholarships in Brazil - Master |