Alcohol Precipitation of Xanthan Gum from Pure Solutions and Fermentation Broths

Abstract

Xanthan gum was precipitated from pure solutions and fermentation broths using either ethanol, isopropanol, or tert-butanol. The compositions of the precipitate and supernatant phases were determined as a function of alcohol concentration and used to construct binodal solubility curves with tie lines. Xanthan did not precipitate at bulk-mixture alcohol concentrations below 37.5% (wt) for ethanol, 35% for isopropanol, and 31% for tert-butanol. As the alcohol concentration increased beyond this point, the precipitates first were heavy gels with low xanthan concentrations. At higher alcohol concentrations, the precipitates were compact and fibrous. The maximum xanthan concentration in the precipitate was 14.5% at 60% ethanol, 23.5% at 50% isopropanol, and 33.5% at 40% tert-butanol in the pure solution precipitation experiments. At alcohol concentrations beyond 75%, the precipitates were brittle and needle-like, which made separation from the supernatant difficult. The results for the fermentation broth experiments were very similar to those of the pure solution experiments. Thus, precipitation using ethanol required the highest alcohol usage and resulted in the lowest xanthan concentration in the precipitate. Conversely, tert-butanol required the least alcohol for precipitation and formed the precipitates highest in xanthan concentration.