Characterisation and solution properties of a galactomannan from Bauhinia monandra seeds

Abstract

This study reports on the chemical and physicochemical properties of the polysaccharide isolated from Bauhinia monandra seeds. The seeds were found to contain 17.8% polysaccharide which consisted predominantly of galactose and mannose. The Man/Gal ratio was found to be approximately 4:1and the average molar mass was 2.54 × 105 g/mol. The extracted material was also found to contain a small amount of protein (5.35%). The galactomannan produced highly viscous solution; the viscosity–shear rate profile was best described by the Williamson model. The mechanical spectrum of a 0.5 wt% solution showed that G″ was greater than G′ over the frequency range employed while at higher concentrations G′ became greater than G″ above a critical frequency. The solutions obeyed the Cox-Merz rule at low concentrations, but there was some deviation at higher concentrations. Viscosity measurements were undertaken over a range of temperatures and the activation energy of viscous flow was found to be 20.75 kJ/mol. The rheological properties of solutions of B. monandra galactomannan indicate that it has comparable characteristics to other commercially important galactomannans such as guar gum and locust bean gum and hence has potential as a thickener in the formulation of food and other related products