Breeding And Identification Of Endoinulinase-producing Strains And Its Fermental Conditions Optimzation

Fructooligosaccharides have significant nutrition and health functions. The research of inulin hydrolysis for fructooligosaccharides production, and the breeding of endoinulinase-producing strains, are hot topics in the study of functional oligosaccharides.â‘ Isolation and identification of endoinulinase-producing strains:With Jerusalem artichoke soil sampled from Northwest University Biological Park, six endoinulinase-producing strains are isolated by the primal screening on agar plates, in which inulin was sole carbon source and melezitose was used as the identification carbon source. After rescreening based on I/S values, two endoinulinase-producing strains with higher I/S values were obtained, and which are labled NCM and NSY5. The initial endoinulinase activities(I/S value) produced by NCM and NSY5 reached 17.82 and 12.41 respectively. Through analyzing and comparing of colony morphology, mycelium and spores morphology, biochemical properties, the strains NCM and NSY5 were identified as Ramularia NCM and Kluveromyces NSY5 preliminarily.â‘¡Fermental conditions optimzation of endoinulinase-producing strains:On the basis of single-factor experiments, eight factors affecting the endoinulinase-producing activity of yeast Kluveromyces NSY5 were evaluated by Plackett-Burman design, the experimental results showed that the medium concentration of jerusalem artichoke juice, loaded liquid and fermentation time had notable influence to the endoinulinase-producing activity. A central composite design Box-Behnken was employed to optimize the significant factors screened and the results were shown in response surface plots. The validation results showed that, with 3.5% jerusalem artichoke juice, loaded liquid 50ml/250ml and 56 hours fermentation time, the I/S value of endoinulinase activity produced by yeast Kluveromyces NSY5 reached 18.29, which has increased 47.50% than that produced in the initial fermentation conditions. The relative error of the I/S value predicted and the experimental verification value was 0.26%.â‘¢Mutation endoinulinase-producing strains:Choosing Kluveromyces NSY5 as starting strain, a mutant named NSY54W was breeded through inducing mutate treatment by ultraviolet light (110 seconds with 20W UV light in 30cm distance) and microwave light(15 minutes). With repeated synergistic mutation treatment, the I/S value produced by Kluveromyces NSY54W increased 32.95% than that of the original strain.