Inulinase

Inulinase a type of hydrolase capable of hydrolyzing β-2, l-d-fructose glucosidic bonds. Microbes secreting inulinase are widely distributed in nature, and there are many All kinds of microorganisms can be secreted. Inulinase can hydrolyze inulin fructose or fructooligosaccharide under certain temperature conditions.

Figure 1. Protein structure of inulinase.

Source

Inulin was first named after it was isolated from Asteraceae. Inulin (inulin) is a d-fructose with furan configuration dehydrated and polymerized by β-2,1 glycosidic bond, and a linear chain of glucose residue (g) connected to the end of fructose residue (f) Structural polysaccharides are the simplest class of fructans, abbreviated as gfn. In addition, it has been reported that inulin also contains a small amount of inulonose, which is a fructan without g at the end. Inulin, also known as inulin, is derived from plants such as Jerusalem artichoke and chicory. It is a functional fructan and the most soluble water-soluble dietary fiber. As a pure natural functional ingredient, inulin has been approved as a nutritional supplement by more than 20 countries in the world, and is widely used in dairy products, beverages, low-fat and low-calorie foods, baked foods, health food.

Classifications

There are different classification methods for inulinase.

• According to inulinase, it is mainly distributed in the cell, cell wall and cell outside of the microorganism, called intracellular enzyme, cell wall binding enzyme and extracellular enzyme, their proportion is mainly influenced by strain, carbon source, temperature and PH.
• It can be divided into endonuclease and exonuclease according to the different ways of acting substrate, or according to the method of inulinase cleaving fructan chain. The size of i/s is usually used to distinguish between endo-inulinase and exo-inulinase, i is the enzyme activity when inulin is used as the substrate, and s is the enzyme activity when sucrose is used as the substrate. It is generally believed that the i/s value of exoinulinase is lower than that of endoinulinase. Endoinulinase hydrolyzes inulin to obtain high-purity fructooligosaccharides, which are often isolated by fungi. Exo-inulin enzymes are distributed in the cell, cell wall, and outside the cell, and it can obtain high-purity fructose by hydrolyzing inulin.
• According to the source, inulinase can be divided into microbial inulinase and plant inulinase.

Functions

Studies have reported that inulinase can act not only on inulin, but also on sucrose and raffinose, and shows higher vitality and hydrolysis capacity. Using Jerusalem artichoke extract or inulin as a carbon source can induce inulinase production, but Jerusalem artichoke extract is better as a substrate. This may be because the extract contains more short-chain polyfructose in addition to inulin, which is more conducive to the growth of the bacteria and hydrolysis by enzymes. That is to say, a certain substrate can induce the production of inulinase, but the use of different carbon sources as substrates has a great influence on the activity of the enzyme. Studies have found that a certain concentration of inulin, maltose and low concentration of fructose can induce the production of inulinase, starch has little effect on inulinase, but glucose can significantly inhibit inulinase activity. It shows that inulinase has substrate specificity.

Applications

Production of high fructose syrup by inulinase Because high fructose syrup is cheap, sweet, refreshing, high in osmotic pressure, good preservation effect, low calorific value, not easy to cause dental caries, and can be used by diabetics, so in the United States, Japan and other developed countries It is widely used in the food and pharmaceutical industries. After the 1970s, countries began to focus on the preparation of fructose by using inulin as a raw material and acid and enzymatic hydrolysis. Although the acid method has high output, it has many by-products, heavy pigments, and is difficult to separate and refine. In the 1980s, researchers from the United States, the French, Bristol-Myers, Canada and other countries began to study the use of inulinase to make fructose. Its process is simple, the conversion rate is high, the product is pure, and the fructose output is high. It can directly produce ultra-high fructose syrup (uhfgs), with fructose content above 90%. To this end, developed countries such as the United States, Britain, Denmark, France, and Canada are conducting research. This shows that inulinase has great potential for development and application in the production of fructose and fructose syrup. Exo-inulinase degradation products are mainly fructose and the proportion of fructose is high. There are many studies on the production of high fructose syrup by inulinase at home and abroad, and China's research is still in its infancy.