Studies On The Mutation Breeding And Fermentation For Gellan Production

Gellan gum is a kind of food gums which has a superior performance as a thickening agent, a suspending agent, a emulsifying agent, and a stabilizer. It has high commercial profits and market prospects. It is also a kind of polysaccharides which is produced by bio-fermentation methods. It has many great features such as low dosage, high transparency, strong aroma release, anti-acid, anti-alkali and so on. It has a wide range of applications in the food industry, pharmaceutical industry, daily chemical industry and paper products industry.In this paper, Pseudomonas elodea was selected to be treated by N+ implantation. A mutant strain named A3-5 which showed high gellan productivity was isolated. Also, gellan fermentation conditions and cultivation medium as well as the subsequent extraction process were optimized too. Main results of this thesis was as follows:(1) Low-energy N+ ion beam implantation was used to screen Pseudomonas elodea. The voltage and vacuum of ion beam implantation was 10 KeV and 10-3 Pa, and the implantation time was 200 s. Ampicillin physiological was also used to explore the mutant strain A3-5 which produced a high level of gellan gum. The gellan production of mutant strain was increased by 25% as compared with the wild strain, and the gel-strength was 950 g/cm2. The mutant strain grew faster than the wild strain, and its viscosity and molecular weight were also improved. The mutant showed a good genetic stability.(2) The composition of fermentation medium and the physical conditions of cultivations were investigated. The optimal concentration of the carbon and nitrogen sources were as follows: sucrose 30 g/L, complex nitrogen sources 2 g/L.( Inorganic nitrogen sources : NaNO3 1 g/L, organic nitrogen: soytone 1 g/L.) Also, physical conditions were gained as follows: the medium volume 120 ml in 500ml shake flask, inoculum size 12%, and pH 7.5. The gellan production and gel-strength were increased by 4.2% and 13.7%, respectively.(3) The down stream process, removal of acetyl as well as protein were investigated. As a result, the gel-strength reached 1270 g/cm2. Two methods of removing protein were compared. The results showed: filtration treatment was better than enzymatic treatment. Its protein removal rate was 86.2% and the recovery rate of gellan was 96.2%.