Xanthan gum production under several operational conditions: molecular structure and rheological properties

Xanthan gum production under several operational conditions has been studie d. Temperature, initial nitrogen concentration and oxygen mass transfer rat e have been changed and average molecular weight, pyruvilation and acetylat ion degree of xanthan produced have been measured in order to know the infl uence of these variables on the synthesised xanthan molecular structure. Al so, xanthan gum solution viscosity has been measured, and rheological prope rties of the solutions have been related to molecular structure and operati onal conditions. The Casson model has been employed to describe the rheolog ical behaviour. The parameter values of the Casson model, tau(o) and K-c, h ave been obtained for each polysaccharide synthesised under different opera tional conditions. Both pyruvilution and acetylation degrees and average mo lecular weight of xanthan increase with fermentation time Lit any operating conditions. Xanthan molecules with the highest average molecular weight ha ve bet Il obtained at 25 degrees C. Nevertheless, at this temperature aceta te and pyruvate radical concentration are lowest, Nitrogen concentration in broth does not show any clear influence over xanthan average molecular wei ght, although with high nitrogen source concentration xanthan with low pyru vilation degree is produced. (C) 2000 Elsevier Science Inc. All rights rese rved.