Characterization of fractional precipitation behavior of galactomannan gums with ethanol and isopropanol

Three galactomannans of guar gum (GG), locust bean gum (LBG) and fenugreek gum (FG) were fractionally precipitated from pure solutions by the addition of either ethanol or isopropanol. The galactomannan precipitates were formed when the bulk solutions containing >18.6% (v/v) ethanol or 13.5% (v/v) isopropanol. The galactomannan recovery of GG, LBG and FG in 33.3% ethanol solvent was 93.1, 86.1 and 94.5%, respectively, while that in 28.8% isopropanol solvent was 94.1, 92.5 and 97.7%, respectively. To achieve the same precipitation efficiency, the usage amount of isopropanol was much lower than that of ethanol, owing to the low dielectric constant for isopropanol (20 vs. 25). It was demonstrated that the precipitation behavior of galactomannans in polar organic solvents was dependent on the molecular structure, such as molecular weight and galactose substitution.