MEDIUM DEVELOPMENT FOR XANTHAN PRODUCTION

Statistical designs were used to determine optimum levels of medium nutrients for xanthan production in shake flask fermentations. Information about the effects of each medium component on xanthan fermentation and the metabolism of Xanthomonas campestris was also obtained. The use of high carbon to nitrogen ratios in the defined medium resulted in a major increase in the broth consistency index. Maximal production was achieved in nitrogen limitation, at a carbon to nitrogen ratio of 23. Mineral sources such as CaCO3 and KH2PO4 proved to be important factors influencing polysaccharide production and quality. A maximum concentration of 11.15 g/litre of xanthan was obtained during the optimization of the defined medium. An increase of xanthan production was accompanied by a decrease of exocellular protein. The addition to the defined medium of yeast extract at a concentration above 0.75 g/litre and peptone above 2.5 g/litre resulted in inhibition of production due to a drop in the carbon to nitrogen ratio. However, if the complex nutrients were added in lower quantities, a slight stimulation of xanthan formation was obtained, 12 g/litre of polysaccharide being achieved.