Ja. Casas et al., Xanthan gum production under several operational conditions: molecular structure and rheological properties, ENZYME MICR, 26(2-4), 2000, pp. 282-291
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.