The pyruvate content of xanthan polysaccharide produced under oxygen limitation

In a recent communication, Suh et al. (1990) considered the batchwise xanthan production in a bubble column with Xanthomonas campestris NRRL B-1459 S4L-II. A polysaccharide with lower mass-mean molar mass was formed when the oxygen supply level (ratio of the oxygen transfer rate OTR to the potential oxygen demand Q sub(O) sub(2)*) of the culture) dropped below one. Using the same synthetic medium in a chemostat, Peters et al. (1990) observed the molar mass to increase with the specific growth rate mu . Since the viscosity yield was determined by the molecular weight, the chemical composition of the product, specifically, the pyruvate content (up to 7.4 wt% for 100% pyruvylation), was not considered in these studies. However, in the application of xanthan for improved oil recovery by polymer flooding, the injectivity may depend mainly on the degree of pyruvylation due to xanthan precipitation or adsorption on the soil (Kleinitz et al., 1989). Xanthan with a low pyruvate content, on the other hand, may not dissolve easily. Although the pyruvate content depends primarily on the appropriate choice of the strain and the medium, it is also important to know whether the operating conditions have an effect on the degree of pyruvylation. It is the purpose of this paper to provide this information.