| Inulin is a polysaccharide of D-fructose joined byβ(2→1) linkages, producing fructooligosaccharides and ultra-high purity fructose syrup directly by one-step method using inulinase. The fructooligosaccharide is a kind of natural functional polysaccharide, it's physiological functions are as follows: improving intestinal microenvironment, controlling blood sugar and blood lipid levels, preventing adiposis and prompting minerals absorption and vitamins biosynthesis. Fructose has many features such as sweetness, high purity flavor, anti-dental caries, it's metabolic pathways was uncontrol by insulin and so on. Currently, there are many kinds of nature microbiology producing inulinase but the high-yielding strains are rare. Three main studies were carried out in this paper to get high-yielding inulinase strains:1. Ultrasound-enhanced extraction of inulin in Helianthus Tuberosus L.To investigate the impact of ultrasound-assisted extraction of inulin from Helianthus Tuberosus L. Experiment design employed single factor experiments and response surface methodology (RSM). A mathematical model was developed and analyzed to describe the relationships between the main factors and the response of the inulin extraction yield. The results of experiments showed that the p value was 0.00021 lower than 0.01 and the R~2 value was 98.94% from the regression model. It indicated that the model was adequate to describe the experimental value. The yield of inilin extracted by ultrasound reached 94.23% at an optimum conditions of the total extraction time 10 minutes, the ultrasonic irradiation mode 15s/6s, the ultrasonic power 750W, the ratio of solvent to material (v/w) was 1:30.15 and extraction temperature 40℃. The extraction yield increased by 26.25 percentage points compared with the Conventional hot water extraction.2. Breeding the strains for producing inulinaseTo obtain a high-yielding inulinase strains, experiment screening the highest yielding inulinase strains from the rhizosphere soil and leaves of Helianthus Tuberosus L. by initial screening, purification and complex screening of shake-flask and identify as the Aspergillus niger. And then mutagenized the selected strains by UV mutagenesis, microwave mutagenesis and chemical mutagenesis. Eventually, it obtained the highest-yielding inulinase mutational strains for the next experiment by microwave mutagenesis. The enzyme activity of the strains was 15.61U/mL, it increased by 78.20% compared to the original strains.3. Research on fermentation conditions of the mutagenic Aspergillus niger for inulinaseThe aim of our research was to establish the optimum polytechnic parameters of the fermentation conditions. First, we worked out the Plackett-Burmen design to find the key factors from the following eight effective factors on fermentation: the content of wheat bran, inulin, peptone, yeast extract, fermentation time, temperature, pH, and inoculum size, the result indicated that the content of wheat bran(p=0.027741), fermentation time(p=0.029919) and pH(p=0.012346) were significant factors for fermentation conditions of the strains. Then these there factors were optimized by Box-Behnken design and we developed a mathematical model to analyze the relationships between the main factors and the response of the enzyme activity. The regression model of experiments showed that p=0.0001﹤0.01 and R~2=99.62%. It indicated that the model was adequate to describe the experimental value. The enzyme activity of the Aspergillus niger reached 20.42U/mL at an optimum conditions of the content of wheat bran 4.64%, fermentation time 81.5h, pH6.0. The enzyme activity production increased from 15.61U/mL to 20.42U/mL, it increased 30.81% compared to non-optimized.
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