Optimizing the production of welan gum by Alcaligenes facalis NX-3 using statistical experiment design

Welan gum is an exopolysaccharide produced by Alcaligenes facalis NX-3. The composition of the medium for the production of welan gum was optimized with a stepwise strategy. Effects of various carbon and nitrogen sources were investigated. Plackett–Burman design was applied to elucidate the key ingredients in the media and the results indicated that the corn starch, cottonseed cake flour have significant effects on welan gum production. Central composite design was employed to search for the optimal concentration of the two key components and the experimental results were fitted to a secondorder polynomial model at a 98% level of significance. By solving the regression equation and also by analyzing the response surface contour plots, the relative high welan gum production (22.85 g l-1) was obtained at the optimal medium combinations and fermentation conditions as corn starch 43.6 g l-1, cottonseed cake flour 4.1 g l-1, 16-h-old inoculum of 3% (v v-1) sizes, initial pH 7.0 and temperature 30oC. These predicted values were also verified by validation experiments.