Effect And Mechanism Of Ultrasound On Inulinase From Aspergillus Niger

Fructooligosaccharides and ultra-high purity fructose syrup can be produced from that inulinase hydrolyzes inulin in certain condition. Recently, the main way to produce inulinase was microbial fermentation, but its low production rate prevented it from being industrialized. As a new physical technology in enzymes production through microbial fermentation, ultrasound has demonstrated good results. This paper will study the Aspergillus niger which is mutagenized by microwave irradiation, to explore the best situation and mechanism of ultrasound on the production of inulinase. It reviews the ultrasonic irradiations with different parameters to get the influence law of ultrasound on high inulinase production by Aspergillus niger, and discusses the mechanism of ultrasound treatment. The contents of this study are as follows:1.Influence of ultrasound irradiation on inulinase production from Aspergillus nigerThe pH, mycelium dryweight and absorbance over fermentation time were evaluated to get the fermentation curve of Aspergillus niger. Noticeable fermentation phases can be defined as follows: 0-16 h were the lag phase, 16-88 h were the logarithmic growth phase, 88-112 h were the stable phase, it got to the decline phase after 112 h.Givien ultrasound irradiation with ferquency of 40 kHz, power 200 W during the fermentation of Aspergillus niger, 4 h was chose as the appropriate ultrasound treatment time in experiments.When fermentation time was 18 h, under ultrasond treatment with frequency of 59 kHz, power 200 W, irridiation time 4 h, inulinase activity decreased by 47.5 %, the lowest. While fermentation time was 54 h, under ultrasound treatment with frequency of 40 kHz, treatment time 4 h, inulinase activity would be increased by 29.3 %.Given ultrasound irradiation with frequencies of 40 kHz, 59 kHz respectively during fermentation, the results showed that giving irradiation at the lag phase and the beginning of the logarithmic growth phase (0-24 h), inulinase activity declined. But irradiated at the late logarithmic growth phase (30-88 h), positive effect could be seen. At the lag phase and the logarthmic growth phase, frequency of 59 kHz showed greater impact than that of 40 kHz, but in the stable phase and decline phase, inulinase activity increased little or decreased.2.The mechanism of ultrasound on Aspergillus niger fermentation producing inulinaseImpact of ultrasound on cell morphology: In power of 200-500 W, given ultrasound irridiation of 200 W, cell morphology changed to nearly circular, cell appearance clear, and no obvious cell debris. With the ultrasonic power increased, uncontinuous contour line could be seen in some cells, cell debris increased. Impact of ultrasound on the cell protein, viscosity, pH, conductivity of culture and cell lethality: Set ultrasound power<350 W, cell protein content and cell lethality of Aspergillus niger increased slowly with ultrasonic power increased, but the viscosity, pH and conductivity of culture decreased, ultrasound showed positive effect on the growth of Aspergillus niger. When ultrasound power>350 W, negative effect of ultrasound on microbal cells increased with power increased, cell protein contents decreased, the viscosity and conductivity of culture decreased but pH and cell lethality increased, ultrasound inhibited the growth of Aspergillus niger.