Characterisation and solution properties of a galactomannan from bauhinia monandra seeds

Authors: NWOKOCHA, LOUIS - Glyndwr University; SENAN, CHANDRA - Glyndwr University; WILLIAMS, PETER - Glyndwr University; Yadav, Madhav

Submitted to: International Journal of Biological Macromolecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2017
Publication Date: 3/27/2017
Citation: Nwokocha, L.M., Senan, C., Williams, P.A., Yadav, M.P. 2017. Characterisation and solution properties of a galactomannan from bauhinia monandra seeds. International Journal of Biological Macromolecules. 101:904-909.

Interpretive Summary: A new carbohydrate polymer with excellent food gum properties has been prepared from the seeds of Bauhina monandra, an ornamental plant. It has been fully purified and characterized. The flow behavior of its solution and its thickening properties have been studied to evaluate its potential use in food products. It forms a very thick (viscous) solution in water, which decreases with heating and mixing at high speed. Such properties make it very useful for mixing in many food products for altering their texture and thickness giving a better mouth feel. This new carbohydrate polymer has comparable properties 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. These findings will be useful for the growers of this ornamental plant, who are trying to obtain additional revenue from its seeds. Commercialization of this material could potentially provide new uses for these seeds, which are waste products and could provide more revenue for their growers and processors.

Technical 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 4:1 and the average molar mass and radius of gyration were 2.02 x 10**5 g/mol and 36.6nm respectively. The extracted material was also found to contain a small amount of protein (5.35%). The galactomannan produced highly viscous solutions and the viscosity for solutions in the concentration range from 0.5 – 2.0 wt % decreased significantly with increasing shear rate. The viscosity – shear rate profile was best described by the Williamson model, with zero shear viscosities of 0.25 to 244 Pa.s over the concentration range studied. 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 Bauhinia 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.