Xylanase Activity – Definition and Relevance

What Is Xylanase Activity?

Xylanase activity refers to the degree to which the enzyme xylanase is capable of cleaving xylans -- complex plant polysaccharides found in the cell walls of plants. Xylanase belongs to the class of hydrolases and catalyzes the hydrolytic cleavage of glycosidic bonds within the xylan backbone.

The activity of this enzyme is typically measured in international units (IU), where one unit corresponds to the amount of enzyme that releases a defined quantity of xylose per minute under standardized conditions. Xylanase activity is commonly determined using standardized substrate assays, often employing birchwood xylan as the substrate.

Origin and Natural Sources of Xylanase

Xylanase occurs naturally in a wide range of organisms:

• Microorganisms: Bacteria (e.g., Bacillus species) and fungi (e.g., Aspergillus niger, Trichoderma reesei) are major natural producers of xylanase.
• Plants: Certain plants produce xylanase during germination or growth processes.
• Animal digestive tract: Microorganisms inhabiting the gut of ruminants and other herbivores produce xylanase as part of their digestive enzyme repertoire.

Relevance in the Food Industry

In food technology, xylanase activity is particularly important in the baking industry. Xylanase is used as a baking enzyme to improve dough processability and bread quality. By breaking down arabinoxylans in wheat flour, xylanase optimizes dough consistency, increases loaf volume, and extends shelf life.

Xylanase activity is also relevant in the paper and pulp industry as well as in bioethanol production, since xylans are a major component of hemicellulose in lignocellulosic raw materials.

Relevance in Animal Nutrition

In animal nutrition, xylanase preparations are widely used as feed additives, especially for poultry and pigs. Cereal-based feeds contain antinutritive xylans that reduce the digestibility of nutrients. By applying xylanase with sufficient activity, these polysaccharides are degraded, intestinal viscosity is reduced, and nutrient bioavailability is enhanced.

Measuring Xylanase Activity

The determination of xylanase activity is typically performed using enzymatic assays:

• DNS Method (Dinitrosalicylic Acid Method): Reducing sugars released during xylan degradation are measured colorimetrically.
• HPLC Analysis: High-performance liquid chromatography allows precise quantification of released xylose units.
• Standardized Protocols: IUPAC and TAPPI standards define reference methods for comparable measurement of enzyme activity.

Factors Influencing Xylanase Activity

Several factors affect the activity of xylanase:

• pH value: Most xylanase enzymes exhibit an optimum pH in the acidic to neutral range (pH 4.5 to 7.0).
• Temperature: Depending on the enzyme source, the temperature optimum ranges from 40 °C to 60 °C. Thermostable variants are particularly sought after for industrial applications.
• Substrate concentration: Higher xylan concentrations lead to increased reaction rates up to a saturation threshold.
• Inhibitors: Certain metal ions or oxidizing agents can inhibit enzyme activity.

References

1. Polizeli, M. L. T. M. et al. (2005): Xylanases from fungi: properties and industrial applications. Applied Microbiology and Biotechnology, 67(5), 577–591.
2. Collins, T., Gerday, C., Feller, G. (2005): Xylanases, xylanase families and extremophilic xylanases. FEMS Microbiology Reviews, 29(1), 3–23.
3. European Food Safety Authority (EFSA): Scientific opinions on xylanase preparations as feed additives. EFSA Journal, available at: www.efsa.europa.eu