In addition to starch, protein, lipid, ash, the main components of baking flour also contains a class of components for non-starch polysaccharides, the most important component is arabinoxylan, the content of this component accounts for about 1.5% to 2.5% of the total amount of flour. Although the content of this ingredient is not high, but it can absorb and lock their own weight 10-15 times the water, so in the baking process can not be ignored.

The role of xylanase in baking

1.1 The mechanism of xylanase in baking

According to the water solubility of arabinoxylan can be divided into: water-soluble arabinoxylan and water-insoluble arabinoxylan, of which water-insoluble arabinoxylan accounts for about 70%~75% of the total content of arabinoxylan. Experimental studies have proved that water-soluble arabinoxylan has a positive effect on bread quality, while water-insoluble arabinoxylan has a negative effect on bread quality.

Xylanase can hydrolyze the (l→4)-β-D-glycosidic bond of arabinoxylan, making the insoluble arabinoxylan turn into high molecular water-soluble arabinoxylan, and further hydrolysis will turn into low molecular water-soluble arabinoxylan.

1.2 The role of xylanase in the bread beating stage

In the process of dough mixing, insoluble arabinoxylan, locking a large amount of water, so that the gluten can not be well formed, and large molecules of insoluble arabinoxylan molecules are not conducive to the stability of the dough.

When using xylanase, during the mixing process of the dough, xylanase decomposes the insoluble arabinoxylan into soluble arabinoxylan and improves the absorption of water; the proper degradation of arabinoxylan makes the viscosity of arabinoxylan attached to the gluten film decrease, which promotes the increase of the dough’s extensibility; the ever-increasing soluble arabinoxylan and the oxidant in the bread oxidation gel The increasing soluble arabinoxylan and the oxidizing agent in the bread will have oxidative gelation, which will increase the water-holding and elasticity of the dough. Therefore, the reasonable addition of xylanase can make the dough feel dry, good ductility, plasticity and good mechanical operability.

But excessive addition of xylanase will make the large molecule soluble arabinoxylan further hydrolyzed into low molecule water-soluble xylan, which will excessively release water, making the dough too soft and sticky, and the mechanical processing performance becomes poor.

1.3 The role of xylanase in bread rising and baking stage

Reasonably added xylanase dough, dryness, elasticity, ductility are better, so that the rise stage has good gas holding and rise tolerance. The baking stage of bread is the continuation of the rising stage, which is the period of rapid expansion of the dough, and the elasticity, ductility and air-holding properties of the dough are very important in this stage, which will be directly related to the final quality of the baked product.

Reasonable addition of xylanase dough into the oven rapid rise good, the volume of baked products increased; elasticity and bubble stability is good, the bread gas holding better, improve the structure of the baked product so that the air holes are uniform, air holes thin wall.

1.4 The role of xylanase on bread end-products

Although xylanase is inactivated in the baking stage of bread, it is an active substance in the dough-beating stage, the rising stage and the early stage of baking, and still has an effect on the baked end product. Aging of bread usually involves two aspects, starch regrowth and moisture migration.

The addition of xylanase can reduce the migration of water in bread, this is because after adding xylanase in the right amount, more soluble arabinoxylan is generated, arabinoxylan can gel with the oxidizing agent in the bread, increasing the water holding properties of the bread and reducing the migration of water in the bread.

Sources and Properties of Xylanases Commonly Used in Flour

2.1 Sources and classifications of xylanases commonly used in flour

Nowadays, xylanases commonly used in flour are all from microbial fermentation, which can be categorized into bacterial xylanases and fungal xylanases according to the fermenting microorganisms. According to whether the genes of fermenting microorganisms have been modified or not, they can be classified into genetically modified xylanase and traditional non-genetically modified xylanase.

2.2 Optimum pH of xylanases from different sources

Fig. Variation of xylanase activity with pH for two xylanases

From the figure, it can be seen that different sources of xylanases are adapted to different pH values, with fungi possessing the best vitality in acidic environments, while bacterial xylanases have a wider pH adaptability and can maintain good vitality in weakly acidic to neutral environments. Therefore, xylanase from suitable source can be selected according to the formulation and process of bakery products.

Conclusion.

The rational addition of xylanase can play the following roles: it can reduce the viscosity of the surface of the baking dough, increase the ductility and elasticity, and thus improve the mechanical operability of the dough; it can increase the volume of the baked end-products; it can improve the organization of the baked end-products, so as to make the wall of the internal air holes of the products thin and uniformly fine; it can reduce the migration of moisture from the baked end-products, thus reduce the loss of moisture in the process of product storage, and Delay the aging of baked products.