Screening of Factors Affecting the Enzymatic Hydrolysis of Empty Fruit Bunches in Aqueous Ionic Liquid and Locally Produced Cellulase System

Authors: Md. Z. Alam, Amal A. Elgharbawy, Muhammad Moniruzzaman, Nassereldeen A. Kabbashi, Parveen Jamal

Abstract:

The enzymatic hydrolysis of lignocellulosic biomass is one of the obstacles in the process of sugar production, due to the presence of lignin that protects the cellulose molecules against cellulases. Although the pretreatment of lignocellulose in ionic liquid (IL) system has been receiving a lot of interest; however, it requires IL removal with an anti-solvent in order to proceed with the enzymatic hydrolysis. At this point, introducing a compatible cellulase enzyme seems more efficient in this process. A cellulase enzyme that was produced by Trichoderma reesei on palm kernel cake (PKC) exhibited a promising stability in several ILs. The enzyme called PKC-Cel was tested for its optimum pH and temperature as well as its molecular weight. One among evaluated ILs, 1,3-diethylimidazolium dimethyl phosphate [DEMIM] DMP was applied in this study. Evaluation of six factors was executed in Stat-Ease Design Expert V.9, definitive screening design, which are IL/ buffer ratio, temperature, hydrolysis retention time, biomass loading, cellulase loading and empty fruit bunches (EFB) particle size. According to the obtained data, IL-enzyme system shows the highest sugar concentration at 70 °C, 27 hours, 10% IL-buffer, 35% biomass loading, 60 Units/g cellulase and 200 μm particle size. As concluded from the obtained data, not only the PKC-Cel was stable in the presence of the IL, also it was actually stable at a higher temperature than its optimum one. The reducing sugar obtained was 53.468±4.58 g/L which was equivalent to 0.3055 g reducing sugar/g EFB. This approach opens an insight for more studies in order to understand the actual effect of ILs on cellulases and their interactions in the aqueous system. It could also benefit in an efficient production of bioethanol from lignocellulosic biomass.

Keywords: Cellulase, hydrolysis, lignocellulose, pretreatment, stability.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1125657

References:

[1] X.-D. Hou, N. Li and M.-H. Zong, "Significantly enhancing enzymatic hydrolysis of rice straw after pretreatment using renewable ionic liquid–water mixtures", Bioresour. Technol., vol.136, no.0, pp. 469-474, Mar 2013.
[2] P. Engel, S. Krull, B. Seiferheld and A.C. Spiess, "Rational approach to optimize cellulase mixtures for hydrolysis of regenerated cellulose containing residual ionic liquid", Bioresour. Technol., vol.115, no.0, pp.27-34, Jul 2012.
[3] J. Xu, B. Wu, L. Hu, Z. Wu, N. Xu, B. Dai and J. He, "Enzymatic in situ saccharification of lignocellulose in a compatible ionic liquid-cellulase system", Chem. Eng. J., vol. 267, pp. 163-169, May 2015.
[4] H. Zhao, G.A. Baker, Z. Song, O. Olubajo, T. Crittle and D. Peters, "Designing enzyme-compatible ionic liquids that can dissolve carbohydrates", Green Chem., vol.10, no.6,pp. 696-705. Apr 2008.
[5] T. Ghose, "Measurement of cellulase activities", Pure and Applied Chemistry, vol. 59, no. 2, pp. 257-268, Jun 1987.
[6] Â.C. Salvador, M.d.C. Santos and J.A. Saraiva, "Effect of the ionic liquid
[bmim] Cl and high pressure on the activity of cellulase", Green Chem., vol. 12, no. 4, pp. 632-635, Feb 2010.
[7] M. Naushad, Z.A. ALOthman, A.B. Khan and M. Ali, "Effect of ionic liquid on activity, stability, and structure of enzymes: a review", Int. J. Biol. Macromol, vol. 51, no.4, pp. 555-560, Nov 2012.
[8] R. Wahlström, S. Rovio and A. Suurnäkki, "Partial enzymatic hydrolysis of microcrystalline cellulose in ionic liquids by Trichoderma reesei endoglucanases", RSC Adv., vol. 2, no.10, pp. 4472-4480, Apr 2012.
[9] X.D. Hou, T.J. Smith, N. Li and M.H. Zong, "Novel renewable ionic liquids as highly effective solvents for pretreatment of rice straw biomass by selective removal of lignin", Biotechnol. Bioeng., vol. 109, no.10, pp. 2484-2493, Oct 2012.
[10] Q. Li, Y.-C. He, M. Xian, G. Jun, X. Xu, J.-M. Yang and L.-Z. Li, "Improving enzymatic hydrolysis of wheat straw using ionic liquid 1-ethyl-3-methyl imidazolium diethyl phosphate pretreatment", Bioresour. Technol., vol. 100, no.14, pp. 3570-3575, Jul 2009.
[11] H.T. Tan, K.T. Lee and A.R. Mohamed, "Pretreatment of lignocellulosic palm biomass using a solvent-ionic liquid
[BMIM]Cl for glucose recovery: An optimisation study using response surface methodology", Carbohydr. Polym., vol. 83, no.4, pp. 1862-1868, Feb 2011.
[12] N.I. Haykir, E. Bahcegul, N. Bicak and U. Bakir, "Pretreatment of cotton stalk with ionic liquids including 2-hydroxy ethyl ammonium formate to enhance biomass digestibility", Ind. Crops Prod., vol. 41, no.31, pp. 430-436, Jan 2013.
[13] N.I. Haykir and U. Bakir, "Ionic liquid pretreatment allows utilization of high substrate loadings in enzymatic hydrolysis of biomass to produce ethanol from cotton stalks", Ind. Crops Prod., vol. 51, no.30, pp. 408-414, Nov 2013.
[14] S. Zhi, Y. Liu, X. Yu, X. Wang and X. Lu, "Enzymatic Hydrolysis of Cellulose after Pretreated by Ionic Liquids: Focus on One-pot Process", Energy Procedia, vol.14, pp. 1741-1747, Mar 2012.
[15] N. Kamiya, Y. Matsushita, M. Hanaki, K. Nakashima, M. Narita, M. Goto and H. Takahashi, "Enzymatic in situ saccharification of cellulose in aqueous-ionic liquid media", Biotechnol. Lett., vol. 30, no.6, pp. 1037-1040, Jun 2008.