Process Optimization Of Welan Gum Production Using Alcaligenes Sp. AtCC31555

Welan gum is a kind of soluble extracellular polysaccharide produced by Alcaligenes(previously named S^-130) and consists of laevoglucose, levorotatory glucose hyaluronic acidand L-rhamnose as its main structure unit. Welan gum in aqueous media has excellentrheological properties, and its special molecular structure has attracted the extensive attentionof food, oil exploitation and building industry. It is one of the most market prospectivemicrobial polysaccharide developed by Kelco, a company of American.Scale-up of welan gum production was limited by the low productivity and high cost.Here the response surface methodology was selected to optimize the extraction condition andoxygen carrier was chose for improving the welan gum yield, at last cane molasses was usedas low carbon source to reduce the fermentation cost. The results are as follows:Firstly, four factors including ethanol-fermentation broth ratio, ethanol concentration,extraction temperature and extraction time were analyzed by univariate analysis and theethanol concentration, ethanol-fermentation broth ratio and extraction time were confirmed asthe significant factor by Plackett-Burman （PB） experimental design. Finally, the optimalcombination of impact of significant factors were as follows: A（alcohol concentration）, B（solid to liquid ratio） and C （extraction time） values were93.75%,2.75:1, and30minrespectively, with welan gum extraction yield14.2g·L^-1. The verification tests showed theextraction concentration of welan gum was13.9±0.14g·L^-1and increased26.36%comparedwith that before optimization。Continuous secretion of welan gum makes broth sticky and dissolved oxygen became alimiting factor. After, n-hexane, n-dodecane, n-hexadecane, Tween-80, Span-80these fiveoxygen carrier were used as oxygen carriers for optimization. Firstly, univariate analysis wasused to determine the optimal concentration of those five oxygen carriers and n-dodecane isthe best oxygen carrier to improve cell biomass and welan gum production, and it was addedinto broth at60h after inoculation. Finally, through Box-Behnken response surfacemethodology, the optimal combination of concentration and addition time of n-dodecaneand pH of the fermentation broth were as follows: A（concentration of n-dodecane）, B（addingtime of n-dodecane） and C（pH） are8.27%、64.2h and7.5respectively. The highest welan gumconcentration was24.3g·L^-1and increased39.41%compared with that without oxygencarrier..Cane molasses was usually used as cheap substrate for bio-chemicals industrialproduction. Some necessary pre-treatment was used for wiping off some inhibitor from original cane molasses. The results showed that the most efficiency pre-treatment is sulfuricacid treatment compared to dilution and active carbon treatment. Maximum welan gumproduction (41.0±1.41g·L^-1) was obtained under the condition of600rpm,30°C with10%N-dodecane at36h in batch fermentation when cane molasses was used as substrate aftersulfuric acid treatment. And it was the highest yield in the literature.