Fermentation Production Process Of Novel Microbial Polysaccharide-welan Gum

Welan gum is a heteropolysaccharide produced by Alcaligenes ATCC 31555(previously named S-130). The unique feature of welan, rheology property and its special molecular structure has attracted the extensive attention of oil well drilling fluids, Building Industry and food industry. In this thesis, we studied fermentation characters of welan; the ideal culture medium and fermentation conditions. The progresses of isolation, purification and separation of welan gum from fermentation broth were studied, and the structure of the purified welan gum which was separated and purified from fermentation broth was analyzed. The rheological property of welan gum solution was studied. The main Results were as following:According to the yield and viscosity of welan gum, the optimal parameters of fermentation were studied. Results showed that the optimal fermentation medium contained: 40g/L sucose,4g/L complex nitrogen (20% sodium nitrate and 80% beef extract), 2g/L KH₂PO₄, 0.1g/L MgSO₄ and 0.5mL/L 0.1% FeSO₄. The optimized condition were: initial pH 7.2～7 .4, inoculation volume 5%, and aeration ratio 1:5(medium volume: flask volume). 30℃for 58h in 250mL shake flasks at 200r/min, the yield of welan gum increased from 9.326g/L to 21.767 g/L. The anaphase of logarithm growth of the strains is 16h～24h, it enter into contabescence about 44h, from that, mycelium biomass declining slowly. Therefore, it should be better to inoculate at 16h～424h, the stagnation of mycelium growth can be avided and fermentation period was shorten.According to pretreatment of the crude Welan gum and farther separation and purification, the analytic sample was obtained. The components of analytic sample were identified by traditional chemical method,TLC,Ion chromatography,IR,and GC-MS, results showed that it contained rhamnose, glucose, mannose, galactose,and glucuronic acid, the respective percentages are 36.06%, 32.58%, 8.98%, 5.28%, 14.33%. The content of saccharide and acetyl is 84.95%,5.8375%, respectively. The polysaccharide was mainly consisting of (3 glucosidic linkages.The rheological property of welan gum solution was studied. It showed that the solution of welan gum is a typical pseudoplastic liquid. Under the external influence of the environment, which has included different temperatures (30℃～121℃), concentration, pH (2～12) and salt (sodium, potassium, calcium, aluminum), viscosity is extremely stable. Welan Gum showed widely applications future compared with xanthan gum.