PHASE-EQUILIBRIA FOR XANTHAN GUM IN ETHANOL WATER SOLUTIONS

An equilibrium phase diagram was developed for the ternary system xanthan/ethanol/water at 15°C and 1% w/v KCl. The data demonstrate that xanthan precipitation by ethanol occurs at ethanol levels of 30% w/w solvent or greater. The effect of ethanol concentration on xanthan solubility is markedly different from that of ethanol on proteins and is characterised by a sudden transition from high solubility to virtual insolubility over a narrow range (20-30% w/w solvent) of solvent-ethanol content. Further increases in ethanol content gave no improvement in xanthan yield but increasing xanthan purity. The applicability of three equilibrium-solubility models commonly used to describe other polymer-solvent systems is discussed. Of these, that based on solution theory appears to be the most useful. The solubility data are used to predict how xanthan recovery from fermentation broths by ethanolic precipitation can be optimised in terms of yield. © 1990.