Xylanase

Xylanase

Xylan is a heterogeneous polysaccharide present in plant cell walls, accounting for about 15% to 35% of the dry weight of plant cells, and is the main component of plant hemicellulose (hemicellose). Most xylan is a complex, highly branched heterogeneous polysaccharide that contains many different substituents. The biodegradation of xylan therefore requires a complex enzyme system to degrade xylan through the synergy of various components. Therefore, xylanase is a group of enzymes, not an enzyme.

Sources of xylanase

Xylanase is widely distributed in nature and can be obtained from animals, plants and microorganisms. For example, xylanase is present in marine and terrestrial bacteria, marine algae, fungi, yeast, rumen and ruminant bacteria, snails, crustaceans, land plant tissues, and various invertebrates. Xylanase of microbial origin is ubiquitous in nature, and has a wide variety of applications in a wide range of fields. Therefore, there are many reports on the research of microbial xylanase. Recently, the most studied and applied xylanase from bacteria and fungi is bacteria. Among them, bacteria can produce alkaline and acid xylanase, while fungi can only produce alkaline xylanase. Filamentous fungi secrete the highest extracellular enzymes. At present, xylanase mainly uses microorganisms such as fungi and bacteria for fermentation production.

Figure 1. Protein structure of xylanase.

Composition of xylanase

Xylanolytic enzyme systems (xylanolyticenzymesystems) is a class of xylan degrading enzyme systems, including β-1,4-endoxylanase, β-xylosidase, α-L-arabinosidase, α- D-glucuronidase, acetylxylanase and phenolate esterase can degrade a large amount of xylan hemicellulose existing in nature. In the xylan hydrolase system, β-1,4-endoxylanase is the most critical hydrolase, which hydrolyzes xylan by hydrolyzing the β-1,4-glycosidic bond of the xylan molecule for small oligosaccharides and xylooligosaccharides such as oligosaccharides, and a small amount of xylose and arabinose. Beta-xylosidase catalyzes the release of xylose residues by hydrolyzing the ends of xylooligosaccharides. In addition, there are α-L-arabinofuranosidase, α-glucuronidase, acetylxylan esterase, and araxylan side chain residues and phenols that can degrade xylan completely. Side chain hydrolases such as phenolic esterases of ester bonds formed by acids (such as ferulic acid or coumaric acid), they act on the glycosidic bond between the xylose and side chain substituents, and cooperate with the main chain hydrolytic enzyme Ultimately converts xylan into its constituent monosaccharides.

Applications

• Application of xylanase in baked food

Xylanase increases the volume of the dough by changing the gluten network structure, which increases the elasticity and ductility of the dough, reduces the dryness, hardness and water retention, reduces the chewability and viscosity, and improves the dough processing and stability performance.

• Application of xylanase in beverage

In the juice production process, too high viscosity is not conducive to juice filtration, too high turbidity will cause the quality of juice to decline. After treatment with xylanase, the filterability of the juice increases (the turbidity of the juice decreases because the xylanase hydrolyzes carbohydrates and polysaccharides present in the crude juice). In addition, the combined use of complex enzymes (such as cellulase) and xylanase can also improve the efficiency of juice extraction.

• Application of xylanase in brewing industry

In the production process of beer, malt contains hemicellulose, which is extremely hydrophilic, which makes it difficult to filter wort and reduces the yield of wort. The addition of xylanase in the brewing process of beer is helpful to reduce the viscosity of wort, improve the yield and yield of wort, and accelerate the filtration rate of wort.

• Application of xylanase in health products

Functional oligosaccharides including xylooligosaccharides are difficult to digest in mammalian small intestine due to lack of corresponding digestive enzymes, but are easily assimilated and metabolized by colonic probiotic microorganisms such as Lactobacillus and Bifidobacterium, so they are used as prebiotics and be concerned. The use of xylanase hydrolysis to prepare xylooligosaccharides has become the main production method of xylooligosaccharides in industry.

Conclusions

Xylanase is widely used as a biocatalyst in the food industry, but the complexity and rapid development of the food industry requires xylanase to be efficient, diverse, and specific Promote. In the past few decades, through the use of a single or comprehensive method (such as high-throughput screening, protein engineering, etc.), the development of high thermal stability, acid and alkali resistance, non-metallic ion dependence, fast reaction speed, substrate utilization High-quality xylanase to meet the actual production needs of the food industry. However, there are still many problems that need to be solved urgently, such as low conversion efficiency of enzymes, high prices, low reutilization rate, poor stability, and narrow substrate action range. Therefore, it is necessary to use the knowledge of basic structural design and basic biochemistry as a guide, and use genetic engineering, protein engineering, biocomputer simulation and high-throughput methods to further target the catalytic properties of xylanase to improve food Quality, reduce production costs and achieve sustainable development.

Reference

1. Subramaniyan S, et al. Biotechnology of microbial xylanases: enzymology, molecular biology, and application. Critical Reviews in Biotechnology. 2002, 22 (1): 33–64.