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The degree of pyruvyiation of the xanthan side chains decreased strongly when the microbial oxygen demand was not met. There was no significant dependence on the growth rate.

An empirical model for the production of xanthan polysaccharide by batchwise cultivation of Xanthomonas campestris was developed. The effects of oxygen depletion in the liquid and bacterial growth rate on the xanthan production rate and the time‐course of the xanthan molar mass were taken into account. When the oxygen transfer was rate limiting in the non‐growth phase, the molar mass of the final xanthan product was lower than that observed in the absence of oxygen limitation. A constant feed of medium, containing citric acid, increased the xanthan productivity and allowed a polysaccharide concentration of 50 kg/m3 to be reached within 57 h. Low productivity observed in a 3 m3 reactor with small‐diameter Rushton turbines was attributed to stagnant zones in the wall region.

Xanthan concentration and molecular weight distribution are determined by size .exclusion chromatography in the fermentation medium after dilution and cell removal by centrifugation. The analysis is rapid enough for process control. During a batch fermentation, the average molecular weight is found to be in the range of Z2-9.3 ~, 106 g/mole and to run through a maximum.

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