Gradient ammonium sulphate fractionation of galactomannans

Water-soluble locust bean and guar gum galactomannans were fractionated by a graded ammonium sulphate precipitation technique. Locust bean gum galactontannans yielded five fractions obtained at 20, 30, 45, 80 and 100% saturation with (NH4)(2)SO4. The yields of the fractions based on the total material recovered after fractionation) were 3.0, 60.0, 23.0, 9.0 and 5.0, respectively. Guar gum galactomannans yielded three fractions obtained at 70, 80 and 100% saturation with (NH4)(2)SO4. The yields were 31.0, 39.0 and 30.0%, respectively. Monosaccharide and [C-13]-NMR analyses revealed differences in structural characteristics among samples. Fractions precipitated at relatively low saturation of (NH4)(2)SO4 had a low degree of galactose substitution and a high frequency, of unsubstituted mannose residue pairs. They also showed high limiting viscosity values. Fractions which required much higher concentration of (NH4)(2)SO4 for precipitation were highly substituted, had low frequency of un substituted mannose pairs and relatively low limiting viscosity values.