Fractional Isolation and Study of the Structure of Galactomannan from Sophora (Styphnolobium japonicum) Seeds

Two fractions (1 and 2) of the galactomannan from seeds of sophora (Styphnolobium japonicum) were isolated using cold and hot aqueous extraction with a total yield of 12.88%. The two fractions differed by the ratio between mannose (Man) and galactose (Gal) residues (4.8 : 1 and 5.3 : 1, respectively) and molecular weight (1190 and 1400 kDa, respectively). Aqueous solutions of these fractions were optically active ([]_D = +4.80° and –3.36°, respectively) and highly viscous ([] 1028.8 and 1211.2 ml/g). ¹³C NMR spectra of both fractions were identical with respect to the number and positions of signals, which indicates that their primary structures were identical. Using chemical and spectroscopic (IR and NMR) methods, it was shown that the galactomannan has a main chain consisting of 1,4--D-mannopyranose, some residues of which (16 and 17% in fractions 1 and 2, respectively) are -galactosylated at the C-6 position. Frequencies of differently substituted mannobiose blocks in the chain, calculated for fraction 1 using NMR spectroscopic data, were 0.13 for the disubstitited blocks Gal(Man–Man)Gal, 0.37 for the sum of monosubstituted blocks Gal(Man–Man) and (Man–Man)Gal, and 0.50 for the unsubstituted block Man–Man.