Inulinase is a kind of hydrolase that can hydrolyze β-2, l-d-fructan glycosidic bond. Inulinase-secreting microorganisms are widely distributed in nature, including various microorganisms in soil, water, and animal digestive tracts. Inulinase can hydrolyze inulin to fructose or fructooligosaccharide under certain temperature conditions.
According to the inulinase in microorganisms mainly distributed in the cell, cell wall and extracellular, respectively called intracellular enzymes, cell wall-binding enzymes and extracellular enzymes. Their proportions are mainly affected by the species, carbon source, temperature and pH. 1. As the temperature increases, the proportion of extracellular enzymes decreases, while the proportion of the other two enzymes increases. 2. When culturing microorganisms with inulin or sucrose as carbon source, the ratio of extracellular enzymes of the former is higher than that of the latter, while the other two enzymes are opposite. 3. Extracellular enzymes are mainly synthesized by fungi, and cell wall-bound enzymes are mainly produced by yeast. 4. Appropriate pH increases cell wall permeability, increases the ratio of extracellular enzymes, and decreases the ratio of the other two enzymes.
According to the different ways of acting on the substrate, or according to the way of inulinase enzyme cutting fructan chains, it can be divided into endonuclease (ec18.104.22.168) and exonuclease (ec22.214.171.124). The size of i/s is usually used to distinguish endo-inulinase and exo-inulinase, where i is the enzyme activity when inulin is used as a substrate, and s is the enzyme activity when sucrose is used as a substrate. It is generally believed that the i/s value of exoinulinase is lower than the us of endoinulinase. Endo-inulinase hydrolysis of inulin can yield high-purity fructooligosaccharides, which are often isolated from fungi. Exo-inulinase is distributed in the cell, cell wall and extracellular, and it can hydrolyze inulin to obtain high-purity fructose.
According to the source inulinase can be divided into microbial inulinase and plant inulinase.
- Thermal stability
In most reports, the optimum temperature of inulinase is between 52 and 64 °C, and 55 to 58 °C is the most suitable.
- The effect of pH on vitality
The optimum pH of inulinase is weak acidity, which is not only safe to operate, but also prevents microbial contamination during use. It is also the most stable pH value of fructose.
3 Substrate specificity
Scientists believe that the key to improving the enzymatic hydrolysis efficiency of inulinase is to improve the enzymatic activity and increase the sensitivity of the substrate to the enzymatic action. According to research reports, inulinase can not only act on inulin, but also on sucrose and raffinose, and show higher activity and hydrolysis ability. Certain substrates can induce inulinase, but using different carbon sources as substrates has a great influence on the activity of the enzyme. The study found that a certain concentration of inulin, maltose and low concentration of fructose can induce the formation of inulinase, starch has little effect on inulinase, but glucose can significantly inhibit the activity of inulinase. It shows that inulinase has substrate specificity.
Inulinase has a wide range of sources. Plants in nature and various microorganisms in soil, water and animal digestive tract can secrete inulinase. There are many types of inulinase derived from microorganisms, with good thermal stability and suitable for fermentation production. According to incomplete statistics, there are 17 genera and remaining species of filamentous fungi that produce inulinase, 10 genera and more than 20 species of yeast, and 12 genera and more than 10 species of bacteria. At present, many researchers are still working on screening new enzyme-producing strains and transforming existing strains to obtain production strains with high enzyme activity and good thermal stability.