Xylanase is an enzyme that plays a central role in breaking down plant cell walls. It specifically targets xylan, the most abundant type of hemicellulose and a major component of nearly all terrestrial plant matter, particularly in woody tissues and cereal grains. Its ability to degrade this complex biomass into simpler sugars has made it an important tool in various biotechnological and industrial processes.
What Xylanase Does: Mechanism and Natural Function
Xylan is a complex polysaccharide built from a backbone of xylose sugar units linked by β-1,4-glycosidic bonds. Xylan is a branched heteropolymer, often having other sugars and chemical groups attached to its main chain. This complex structure makes xylan difficult to break down, which is why specialized enzymes are required. Xylanase, specifically endo-1,4-β-xylanase, works by randomly cleaving the β-1,4 linkages within the xylan backbone.
The enzyme performs a process called hydrolysis, which uses a water molecule to break the chemical bond connecting the xylose units. This action results in the production of smaller molecules, primarily xylo-oligosaccharides (XOS), which are short chains of xylose, and the monosaccharide xylose itself. In nature, this depolymerization is how microorganisms access the carbon and nutrients locked within plant biomass. The resulting xylose can be metabolized by these organisms, and the XOS can act as prebiotics with health benefits.
Where Xylanase Comes From
Nature’s primary degraders of plant material are microorganisms, and they are the main source of xylanase enzymes. Fungi and bacteria are the most prolific producers of xylanase, as they rely on these enzymes to dismantle plant cell walls for survival. Common fungal sources include species from the Aspergillus and Trichoderma genera, which are known for their high enzyme production capabilities. Bacterial sources are also numerous and often provide enzymes with unique properties, such as stability at high temperatures or extreme pH levels.
For commercial production, these high-performing microbial strains are cultivated in large bioreactors using a process called submerged fermentation. This method allows for the consistent and cost-effective production of large quantities of the enzyme. The genetic material of many xylanase-producing organisms has been studied, and this knowledge is used to optimize strains for industrial purposes, ensuring the enzyme is both highly active and stable under various processing conditions. The resulting product is often an extracellular enzyme, meaning the microorganism naturally secretes it into the surrounding environment.
Xylanase in Industry: Applications for Food and Feed
The ability of xylanase to break down complex carbohydrates has led to its extensive use across the food and agricultural sectors.
Baking Industry
In the baking industry, xylanase is routinely added to wheat flour dough to improve its handling and the final quality of the baked product. Wheat flour contains arabinoxylan, a type of hemicellulose that can interfere with the gluten network and water absorption. By converting the water-insoluble arabinoxylan into a water-soluble form, xylanase improves dough rheology. This leads to a dough that is less sticky and more manageable. This action also increases the bread’s volume and results in a softer texture with a better crumb structure.
Animal Feed
Xylanase is widely used as an additive in animal feed, especially for poultry and swine, to enhance the nutritional value of grains. Plant-based feed contains non-starch polysaccharides, which are largely indigestible by monogastric animals and increase the viscosity of the gut contents. The enzyme breaks down these components, reducing the gut viscosity and allowing the animals to better absorb nutrients. This leads to improved feed efficiency and overall animal growth, while simultaneously reducing the amount of undigested matter excreted, which lowers environmental waste. The enzyme is also employed in fruit juice clarification and brewing to break down plant cell wall components, which improves filtration and the clarity of the final liquid product.
Xylanase in Sustainability: Pulp, Paper, and Biofuels
Xylanase plays a significant role in industrial processes focused on environmental sustainability, particularly in the pulp and paper industry.
Pulp and Paper Bio-bleaching
The traditional method for removing residual lignin—the substance that gives paper pulp its brown color—involves using harsh, chlorine-based chemicals. Xylanase is now used in a process called bio-bleaching, which serves as an environmentally friendlier alternative or pretreatment. The enzyme targets and hydrolyzes xylan that has redeposited on the surface of the pulp fibers, which physically traps the lignin. By breaking down this xylan barrier, the enzyme loosens the fiber structure and allows subsequent chemical bleaching agents to penetrate more easily and work more efficiently. This enzymatic step significantly reduces the required amount of chlorine compounds, lowering the formation of toxic organochlorine pollutants in wastewater.
Biofuel Production
The enzyme’s ability to dismantle plant biomass also makes it a key component in the production of second-generation biofuels. Xylanase works alongside other enzymes to break down lignocellulosic biomass, such as agricultural waste and wood chips, into fermentable sugars like xylose. This process is a foundational step in converting non-food plant waste into bioethanol and other renewable energy sources.