The Xylanase Enzyme: Functions and Applications
Learn about the xylanase enzyme, a natural catalyst that deconstructs plant cell walls by targeting xylan for applications in food and industrial systems.
Xylanase is a naturally occurring protein that functions as a biological catalyst. This enzyme acts like molecular scissors to cut a substance known as xylan. It breaks down the complex polysaccharide beta-1,4-xylan into a simpler sugar called xylose. This ability makes the enzyme useful across a wide range of industrial processes.
The Source and Function of Xylanase
For industrial purposes, xylanase is primarily sourced from microorganisms like fungi and bacteria. Fungi from the Aspergillus and Trichoderma genera are effective producers because they secrete large amounts of the enzyme. These microorganisms are widespread in nature, found in soil and on decaying plant material.
In their natural environments, these microbes use xylanase to break down tough plant matter to access nutrients. The enzyme’s target is xylan, a major type of hemicellulose, which is the second most abundant polysaccharide in nature and a main component of plant cell walls. This natural function of dismantling plant fiber is harnessed for commercial applications.
Mechanism of Action
The interaction between xylanase and its target molecule follows a “lock and key” model. The enzyme has a uniquely shaped active site that precisely fits the structure of the xylan molecule. This specificity ensures that the enzyme only acts on xylan.
Once bound, the enzyme initiates a chemical reaction called hydrolysis. Using a water molecule, xylanase cleaves the beta-1,4-glycosidic bonds that link individual xylose sugar units. This process dismantles the large polymer into smaller, soluble fragments.
Applications in Food Processing and Animal Feed
In the baking industry, xylanase is used to improve the quality of dough and the final baked product. Flour, particularly from wheat, contains non-starch polysaccharides called arabinoxylans, which can negatively affect dough properties. Xylanase breaks down these arabinoxylans, which releases water that was bound within their structure. This action makes the dough less sticky and improves its handling and machinability.
The enzymatic modification of the dough’s structure leads to benefits in the finished product. The improved gas retention in the dough results in a greater loaf volume and a more uniform, finer crumb structure. This process contributes to a softer texture and can extend the shelf life of bread by slowing the staling process.
Xylanase serves as a clarifying agent in the production of juices, wine, and beer. Xylan polysaccharides in fruit and grain pulps can cause unwanted haze or turbidity in the final beverage. By breaking down these complex carbohydrates, xylanase helps to produce a clearer, more stable liquid. In juice production, its use can also increase the overall yield by facilitating more efficient extraction from the fruit pulp.
For animal feed, particularly for monogastric animals like poultry and pigs, xylanase is a helpful additive. These animals lack the endogenous enzymes needed to efficiently digest the fibrous components, such as xylan, found in common grain-based feeds like corn, wheat, and barley. The presence of these non-starch polysaccharides can trap valuable nutrients and increase the viscosity of the material in the digestive tract, hindering absorption.
Adding xylanase to the feed breaks down these indigestible fibers directly in the animal’s gut. This process releases the encapsulated nutrients, making them available for the animal to absorb. The reduction in viscosity within the gut improves feed passage and overall nutrient utilization, leading to better feed efficiency and growth performance. The breakdown of xylan can also produce prebiotic xylo-oligosaccharides, which support beneficial gut bacteria.
Role in Papermaking and Biofuel Production
In the pulp and paper industry, xylanase is a component of a more environmentally friendly bleaching process known as bio-bleaching. During the production of paper, wood pulp must be bleached to remove residual lignin, the compound that gives wood its rigidity and brown color. Traditionally, this process has relied on chlorine-based chemicals, which can produce harmful organochlorine compounds as byproducts.
Xylanase offers an alternative by targeting the hemicellulose that binds lignin to cellulose fibers in the wood pulp. The enzyme does not directly attack the lignin; instead, it breaks down the xylan network that traps lignin molecules within the pulp. This pre-treatment makes the pulp more permeable, allowing the lignin to be removed more easily in subsequent bleaching stages with significantly fewer harsh chemicals. This reduces the environmental impact of paper production.
The enzyme is also used in the production of cellulosic ethanol, a type of biofuel derived from non-food plant biomass like wood chips, corn stover, and agricultural waste. A major challenge in producing this biofuel is breaking down the rigid structure of plant cell walls to release fermentable sugars. Lignocellulosic biomass is a complex matrix of cellulose, hemicellulose, and lignin.
Xylanase performs a function in the pretreatment of this biomass by specifically hydrolyzing the hemicellulose component, which is primarily xylan. This enzymatic degradation breaks apart the plant fiber structure, exposing the cellulose fibers. Once the cellulose is accessible, other enzymes can then act upon it to produce glucose, which is fermented by yeast into ethanol. Xylanase is part of the enzymatic toolkit used to convert tough plant matter into renewable fuel.