Characterization of Galactomannan Gum from Fenugreek (Trigonella foenum-graecum) Seeds and Its Rheological Properties

Abstract

Galactomannan, a water-soluble heteropolysaccharide, was isolated from the seed of Chinese traditional medicine fenugreek. The polysaccharide was characterized by using both chemical and chromatographic procedures, as well as FT-IR, 1H NMR, 13C NMR spectroscopy. The results showed that the polysaccharide consists of D-mannopyranose and D-galactopyranose residues with a molar ratio of 1.2:1.0. The main chain of this galactomannan comprises β-(1,4)-linked D-mannopyranose residues, in which 83.3% of the main chain is substituted at C-6 with a single residue of α-(1,6)-D-galactopyranose. The galactomannan had a molecular weight Mw of 3.23 × 105 g mol−1 and an intrinsic water viscosity of 235 mL g−1. Fenugreek gum (seed endosperm) contains 73.6% galactomannan. The viscosity of fenugreek gum at 1% concentration is 286 mPa.s (30°C, 170 s−1). The viscosity of the solutions decreased sharply as the rate of shear increased, but rose with increased concentration, and decreased as the temperature of fully hydrated gum solution was gradually raised from 30 to 90°C. Fenugreek gum can be a highly efficient water-thickening agents and can be used in food industry and drug delivery formulations.