Synergism of enzymes in chemical pulp bleaching from an industrial point of view: A critical review

Abstract

Enzymes are biological catalysts and are very specific, catalyzing either a single chemical reaction or a limited number of closely related reactions. For example, xylanases are enzymes that catalyze the cleavage of polymeric xylan and thereby break down this hemicellulose. The first xylanase enzyme preparations used in the bleaching process of chemical pulp also contained cellulase, which catalyzes the hydrolysis of cellulose. This obviously had an adverse effect on pulp yield and quality. Unfortunately, this setback gave enzyme-assisted pulp bleaching a negative reputation. At a later stage, enzyme producers managed to engineer enzyme production strains that generated cellulase-free xylanase preparations. However, due to the initial negative experiences with the earlier enzyme mixtures, only a limited number of companies in the pulp industry have seriously considered using these so-called second-generation enzymes in their bleach plants. It is apparent that these improved enzyme preparations would bring about significant benefits in terms of chemical cost savings and effluent quality. In addition to xylanaseaided bleaching, it is possible to improve the effectivity further by adding other enzymes, such as lipase and esterase, to create an enzyme cocktail. This may be particularly beneficial in the bleaching of hardwood pulp, such as white birch, which often encounters complex and troublesome problems with wood extractives. By adding different types of enzymes at more than one position in the fiberline, even further improvements are possible. The main objective of this review is to discuss the advantages of incorporating modern enzyme preparations in the bleaching of chemical pulp.

Enhancing the efficiency and functionality of xylanase from Bacillus sp. RTS11: Optimization, purification, characterization, and prospects in kraft pulp bleaching

“…Xylanases produced by thermophilic bacterial systems offer distinct advantages. They can withstand higher temperatures and exhibit a broader range of optimal pH values, which makes these enzymes stable and highly suitable for various industrial applications [80]. As a result, Bacillus strains have garnered attention as attractive candidates for producing substantial quantities of extracellular xylanases that remain active under high temperatures and alkaline pH conditions [68].…”

“…Different species of Bacillus are recognized for their ability to secrete xylanases devoid of cellulase activity such as Bacillus pumilus, Bacillus licheniformis, Bacillus subtilis, Bacillus polymyxa, Bacillus amyloliquefaciens, Bacillus brevis, Bacillus circulans, Bacillus stearothermophilus, Bacillus aerophilus [79]. Mushrooms are particularly interesting producers of xylanases; they produce considerable levels of xylanases, but generally, this production is accompanied by high cellulase activity, which deteriorates the quality of the fibers [80].…”

Sustainable and Eco-Friendly Production of Xylanase and Other Enzymes from Tomato Paste through Solid-State Fermentation Using Bacillus safensis MABS6

“…Xylanases that exhibit favorable pH tolerance and thermotolerance have shown promise for use in numerous industrial processes (Tiwari et al, 2022). The utilization of xylanase enzymes is prevalent in the paper and pulp industry, particularly in the bleaching of kraft pulp (Immerzeel & Fiskari, 2023). To meet industrial standards, two approaches are commonly employed for obtaining xylanase: harnessing natural microbial diversity or utilizing genetic engineering methods to enhance xylanase synthesis in host cells (Yin et al, 2010;Khandeparker et al, 2017).…”

Enhanced Xylanase Production from Bacillus safensis MABS6 using Sorghum Straw Substrate: Optimization, Characterization, and Biotechnological Applications

“…The greatest barrier to commercial application of xylanases is its high production cost. Industrial enzyme production is impossible due to the high cost of purified substrates (Immerzeel and Fiskari, 2023). Research on cost-effective substrates for efficient enzyme synthesis, such as agricultural waste, is imperative (Sadh et al, 2023).…”