New studies on gum ghatti (Anogeissus latifolia) part I. Fractionation, chemical and physical characterization of the gum

This paper describes the fractionation, chemical and physical characterization of processed gum Ghatti (Gatifolia SD), and identifies the source of its surface activity. Four fractions were separated using the gradual ethanol precipitation method. With the increase of alcohol concentration, the chemical composition of the fractions exhibited a pattern: arabinose content increased, but the galactose, protein and uronic acid contents decreased in the order of: F50 (50% ethanol precipitate), F65 (65% ethanol precipitate), F80 (80% ethanol precipitate) and FS (the supernatant after 80% ethanol precipitation). Rheologically gum ghatti and its fractions exhibited Newtonian flow behavior until gum concentrations reached to 20% (w/v), at which point gum ghatti showed some shear thinning. At the same shear rate and concentration, the apparent viscosities of these fractions decreased in the order: F50 > F65 > F80 > FS. When compared at same concentration, the FS fraction had the highest surface activity relative to the Gatifolia SD, the other fractions and even gum Arabic. Monosaccharide composition and preliminary structural analysis showed that the branching of the polymer increased in the order of F50, F65 and F80. The degree of branching levels, protein and uronic acid content could be responsible for the different solubility of the fractions in alcohol. However, the molecular structure of FS is significantly different from the other fractions. FT-IR spectroscopy revealed no esterified carboxyl group in gum ghatti. Detailed structural elucidation of each fraction will follow. (C) 2010 Elsevier Ltd. All rights reserved.