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

Author:
Vinod, V.T.P., Sashidhar, R.B., Sarma, V.U.M., Vijaya Saradhi, U.V.R.
Source:
Journal of agricultural and food chemistry 2008 v.56 no.6 pp. 2199-2207
ISSN:
0021-8561
Subject:
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
Abstract:
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.
Agid:
726993