Characterisation of Prosopis juliflora seed gum and the effect of its addition to k-carrageenan systems

The galactomannan from Prosopis julifora (PJ galactomannan) was extracted from milled seeds in water at 50 degrees C. Its structural and solution properties were characterised in comparison with a commercial sample of guar gum (GG galactomannan). After partial degradation, the resulting samples were submitted to C-13-NMR spectroscopy. The mannose to galactose (M/G) ratios of PJ (M/G = 1.64) and GG (M/G = 1.85) galactomannans were estimated from the relative peak areas of the corresponding C-1 lines. Expansion of the C-4 lines revealed differences in the fine structure of the two galactomannans. The intrinsic viscosity determined for the GG sample, [eta] = 10.3 dL g(-1), was slightly higher than that determined for PJ galactomannan, [eta] = 9.4 dL g(-1). Dynamic experiments carried out at the same concentrations showed similar viscoelastic behaviours for the two gums. No enhancement in the storage modulus (G') was observed for kappa-carrageenan/PJ mixed solution in 0.1 mol L-1 KCl at 1.0 g L-1 total polymer concentration, in relation to K-carrageenan alone. Self-supporting gels obtained by mixing K-carrageenan and PJ or GG galactomannans in 0.25 mol L-1 KCl at 10 g L-1 total polymer concentration displayed similar mechanical properties.