Mechanistic investigation of the effect of endoglucanases related to pulp refining

Martin Nagl,Florian Bausch,Oskar Haske-Cornelius,Georg M Guebitz,Gibson S Nyanhongo,Alessandro Pellis,Wolfgang Bauer,Lukas Skopek

doi:10.1007/s10570-021-04386-5

Abstract

Endoglucanases are increasingly being touted as the ultimate solution for reducing energy consumption during the refining process in the pulp and paper industry. However, due to the high variety of endoglucanases in different enzyme formulations, these perform heterogeneously when applied to different pulps. In this study, the effect of four endoglucanases on softwood and hardwood pulp was studied using confocal laser scanning microscopy (CLSM) after addition of fluorescently labelled carbohydrate binding modules (CBMs). Nuclear magnetic resonance (NMR) analysis and high-performance liquid chromatography quantification of released oligo- and monosaccharides was performed for in-depth mechanistical investigation. Changes in the crystallinity levels caused by enzymatic degradation of amorphous regions were monitored by incubation with two different CBMs from Caldicellulosiruptor bescii and from Thermobifida fusca with high preference to either amorphous or crystalline regions of cellulose, respectively. When dosed at identical activity on the endoglucanase specific CellG5 substrate, CLSM analysis indicated the highest decrease of amorphous regions for those endoglucanases which were also most active in laboratory refining trials and which released highest amounts of cellooligomers from pulp. Using 13C-NMR analysis, an increase in para-crystalline cellulose caused by enzyme application was observed. Release of reducing sugars was determined at identical CellG5 dosage, indicating a high variance between the enzymes, especially when complex enzyme formulations were used. Scanning electron microscopy images were obtained for visualization of the endoglucanase activity. The results of mechanistical studies indicate that reduction of amorphous moieties of pulp by endoglucanases is especially beneficial for the refining process.

Highlights

Cellulose is a highly abundant material, used for various processes like paper or textile production
The principal drawback of currently applied refining technologies is the high unit energy consumption, usually ranging from 150 to 500 kWh/ ton paper and accounting for 30–50% of the total energy used for paper making and generation of high amounts of fines (Loosvelt 2009; Lecourt et al 2010; Buzala et al 2016) the use of enzymes during pulp refining emerged as a new measure to reduce energy consumption, resulting in energy savings up to 40% (Fleiter et al 2012; Torres et al 2012; Tripathi 2019; Haske-Cornelius et al 2020)
The action of various endoglucanases which were beneficial in refining of softwood and hardwood pulp was mechanistically studied

Summary

Introduction

Cellulose is a highly abundant material, used for various processes like paper or textile production. Refining of pulps is a key step in the paper making process aimed at increasing fiber–fiber interaction, and positively affects homogeneity, flexibility, tensile index, internal bond, tensile energy absorption and many other characteristics, which result in paper with desired properties (Gharehkhani et al 2015; Reza et al 2019; Tripathi 2019). The principal drawback of currently applied refining technologies is the high unit energy consumption, usually ranging from 150 to 500 kWh/ ton paper and accounting for 30–50% of the total energy used for paper making and generation of high amounts of fines (Loosvelt 2009; Lecourt et al 2010; Buzala et al 2016) the use of enzymes during pulp refining emerged as a new measure to reduce energy consumption, resulting in energy savings up to 40% (Fleiter et al 2012; Torres et al 2012; Tripathi 2019; Haske-Cornelius et al 2020). Endoglucanases attack the cellulose chain internally by cleaving the β- 1,4-linkage between the glucose chains and have a high affinity for the amorphous part of cellulose, thereby increasing the overall crystallinity(Mansfield and Meder 2003; Miotto et al 2014; Kamppuri

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Conclusion