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Compositional Analysis and Rheological Properties of Gum Kondagogu (Cochlospermum gossypium): A Tree Gum from India

Vinod, V.T.P., Sashidhar, R.B., Sarma, V.U.M., Vijaya Saradhi, U.V.R.
Journal of agricultural and food chemistry 2008 v.56 no.6 pp. 2199-2207
plant exudates, chemical composition, viscoelasticity, shear strength, plant products, Cochlospermum, aqueous solutions, galactose, high performance liquid chromatography, modulus of elasticity, rhamnose, gels, polymers, mass spectrometry, uronic acids, India
Gum kondagogu (Cochlospermum gossypium) is a tree exudate gum that belongs to the family Bixaceae. Compositional analysis of the gum by HPLC and LC-MS revealed uronic acids to be the major component of the polymer (approximately 26 mol %). Furthermore, analysis of the gum by GC-MS indicated the presence of sugars such as arabinose (2.52 mol %), mannose (8.30 mol %), α-D-glucose (2.48 mol %), β-D-glucose (2.52 mol %), rhamnose (12.85 mol %), galactose (18.95 mol %), D-glucuronic acid (19.26 mol %), β-D-galactouronic acid (13.22 mol %), and α-D-galacturonic acid (11.22 mol %). Gum kondagogu, being rich in rhamnose, galactose, and uronic acids, can be categorized on the basis of its sugar composition as a rhamnogalacturonan type of gum. The rheological measurements performed on the gum suggest that above 0.6% (w/v) it shows a Newtonian behavior and shear rate thinning behavior as a function of gum concentration. The viscoelastic behavior of gum kondagogu solutions (1 and 2%) in aqueous as well as in 100 mM NaCl solution exhibits a typical gel-like system. The G' (viscous modulus)/G'' (elastic modulus) ratios of native gum kondagogu (1 and 2%) in aqueous solution were found to be 1.89 and 1.85 and those in 100 mM NaCl to be 1.54 and 2.2, respectively, suggesting a weak gel-like property of the polymer. Crossover values of G' and G'' were observed to be at frequencies of 0.432 Hz for 1% and 1.2 Hz for 2% for native gum in aqueous condition, indicating a predominantly liquid- to solid-like behavior, whereas crossover values of 2.1 Hz for 1% and 1.68 Hz for 2% gum in 100 mM NaCl solution suggest a larger elastic contribution.