Compound Screening On High-producing And Low Pigment Pullulans Strain And Fermentation Condition Research

Pullulan was made by Aureobasidium pullulans in the fermentation process glucose metabolism in the use of the exopolysaccharide, the elements for the three-malt sugar, that is, from a-1, 4 glucoside bond connecting the three glucose to form three malt sugar, and then through a-1, 6 glucoside three key malt sugar will be connected to form a neutral linear high molecular weight polysaccharides.The ratio of a-1, 4 glucoside bond and a-1, 6 glucoside bond ratio is 2:1. For this feature, pullulan polysaccharide has advantages of good film, plasticity, viscoelastic, colorless, tasteless, anti-oil, gas-tight and strong, easily biodegradable , and nonhazardous to the humans and the environment. It was widely used in medicine, food, cosmetics, tobacco and other industries.In this paper, preliminary study on the original strain pullulan GS01 was conducted , mainly including strains morpHological characteristics and productive studies, in order to have adequate preparations for the next step mutation breeding.A slide culture of the GS01 strains was observated. For the purpose of polysaccharide.,the state of fermentation and growth curve of GS01 strains showed its fermentation period was six days.The ultraviolet radiation and nitrite were used to treat parental pullulans strain GS01 two times, and then a mutant strain GS₂28, which was pullulan yield higher one time than GS01 and pigment-free or reduced pigments, was obtained. Compared the colony characteristicses between GS₂28 and GS01, the colony size, texture and color of GS₂28 were obviously better than GS01. Genetic stability test of GS₂28 was subcultured 10 generations: fermentation fluid final color white, pH value 3.4-3.6, absorbency 0.185-0.209 and polysaccharide yield 30.11-31.09g/L, indicated that mutant strain GS₂28 was stable, may apply in the actual production.Mutation of the strain GS₂28 study:the start of mutation of the strain GS₂28 state of fermentation, its fermentation characteristics of the study of nutrition conditions on the medium mutation of the strain GS₂28; mutation of the strain GS₂28 culture test; lure Variable strain GS₂28 optimization of the fermentation conditions, and were on the mutation of the strain GS₂28 culture medium and orthogonal test conditions, to choose the best conditions.Fermentation conditions of mutant strain GS₂28 including culture medium and culture conditions was investigated. Finally the optimal fermentation culture medium of GS₂28 were: granulated sugar 60 g/L, yeast extract 0.4 g/L, (NH₄)₂SO₄ 0.6 g/L, KH₂PO₄ 8 g/L, MgSO₄·7H₂O 0.2 g/L, NaCL 4 g/L.The optimal fermentation culture conditions were: culture temperature 30℃,initial pH 7.0,seed age 36 h,liquid medium volumes 80ml/500ml,inoculated volumes 5%, rotate speed 180 rpm,fermentation time 5d.The thesis screening of high-yield and low-pigment pullulan strain; using modern microbiology mutation breeding techniques, in order to adapt the pullulan industrial fermental production .Through the optimization of culture medium and culture conditions of mutant strains, pullulan yield was further improved,which has theoretic and practical significance.