Enzymatic modification of lignosulfonates

Stefan Ortner, Daniela Huber, Gibson S. Nyanhongo, Georg Gübitz, Karin Hofer, Wolfgang Bauer

Research output: Contribution to conferenceAbstractResearch

Abstract

Lignosulfonates are byproducts of the wood pulping process using sulfite. The delignification with sulfides involves acidic cleavage of ether bonds of the lignin resulting in polydisperse products with molecular weights between 1000–140,000 da [1].

In order to increase its modifications to improve reactivity and dispersion properties using oxidative enzymes e.g. laccases are gaining both industrial and scientific interests. Laccases (benzenediol: oxygen oxidoreduc-tases, EC.1.10.3.2) are multicopper containing enzymes that catalyze the oxidation of various aromatic com-pounds (producing reactive species), especially phenolic compounds, concomitantly reducing molecular oxy-gen to water [3]. The generated reactive species enhance the reactivity of molecules/polymers and provide ideal sites for cross-linking leading to polymerization reactions and consequent formation of new materials or materials with new properties.

Further, the discovery of laccase mediators, (molecules which when oxidized by laccases form highly reactive oxidizing species), which have the ability to oxidize substrates which would rather be difficult to oxidize with the enzyme alone, have expanded applications of these enzymes in modifying “inert” polymers.

In this study we investigate the possibility of modifying lginosulfonates, also in the presence of different me-diators.

Myceliopthera thermophila laccase alone was able to oxidize the lignosulfonates to different extents under different pH conditions. The fluorescence intensity steadily decreased during incubation time. The highest decrease in fluorescence intensity (corresponding to 31 %) was achieved at pH 7 during 5000 min of incuba-tion. Previous studies using laccases from different sources also demonstrated this decrease in fluorescence intensity [2,5].

Since extensive oxidation of the lignosulfonates occurred at pH 7, subsequent reactions with different media-tors were also performed under these conditions. However, in all lignosulfonates incubated with mediators, a remarkable 70 % decrease in fluorescence intensity was observed. This shows that the mediators enhance the modification of lignosulfonates which also reduce the needed incubation time.

Anyhow, we also demonstrate for the first time that oxygen as an essential electron acceptor is limiting in laccase mediated oxidation of lignin processes. Oxygen levels decreased to undetectable levels and remained undetectable for a long period in shaking samples without external oxygen supply. However, despite a general increase in molecular weight in all laccase treated lignins, pure oxygen supply does not always lead to the highest Mw. For example Mg-lignosulfonates treated with Trametes villosa laccase under shaking conditions without external oxygen supply had the highest Mw 85777 kDa as compared to 68842 kDa in the presence of pure oxygen. This study therefore demonstrates the importance of supplying oxygen to laccase mediated reactions in order to shorten the incubation time and ensure complete oxidation.


Acknowledgements
The authors would like to thank the Austrian K-Project funding for Future Lignin and Pulp Processing Re-search (FLIPPR) project.

References
1 Lebo S, Gargulak J and McNally T (2001) Lignin. Kirk-Othmer Encyclopedia of Chemical Technology. John Wiley and Sons Inc.
2 Nugroho Prasetyo E, Kudanga T, Rencoret J, Gutiérrez A, del Río JC, Santos JI, Nieto L, Jiménez-Barbero J, Martínez AT, Li J, Gellerstedt G, Lepfire S, Silva C, Kim SY, Cavaco-Paulo A, Seljebakken Klausen B, Frode Lutnaes B, Nyan-hongo GS, Guebitz GM (2010) Polymerisation of lignosulfonates by the laccase-HBT (1-hydroxybenzotriazole) sys-tem improves dispersibility. Biores. Technol. 101: 5054-5062
3 Nyanhongo GS, Nugroho Prasetyo E, Herrero Acero E, Guebitz GM (2012) Advances in the application of oxidative enzymes in biopolymer chemistry and biomaterial research In: Felber F. et al. eds. “Functional Materials from Re-newable Sources”, ACS symposium series, American Chemical Society Washington DC, 2012, pp 329 - 349
4 Nugroho Prasetyo E, Kudanga T, Fischer R, Eichinger R, Nyanhongo GS, Guebitz GM (2012) Enzymatic synthesis of lignin-siloxane hybrid functional polymers. Biotech. J. 7: 284–292
Original languageEnglish
Publication statusPublished - 12 May 2016
EventPaper and Biorefinery Conference - Messecenter Graz, Graz, Austria
Duration: 11 May 201612 May 2016

Conference

ConferencePaper and Biorefinery Conference
CountryAustria
CityGraz
Period11/05/1612/05/16

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Fields of Expertise

  • Advanced Materials Science

Cite this

Ortner, S., Huber, D., Nyanhongo, G. S., Gübitz, G., Hofer, K., & Bauer, W. (2016). Enzymatic modification of lignosulfonates. Abstract from Paper and Biorefinery Conference, Graz, Austria.