Water-soluble locust bean and guar gum galactomannans were fractionate
d by a graded ammonium sulphate precipitation technique. Locust bean g
um galactontannans yielded five fractions obtained at 20, 30, 45, 80 a
nd 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. Th
e 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 freq
uency, of unsubstituted mannose residue pairs. They also showed high l
imiting viscosity values. Fractions which required much higher concent
ration of (NH4)(2)SO4 for precipitation were highly substituted, had l
ow frequency of un substituted mannose pairs and relatively low limiti
ng viscosity values.