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

Edwin G. Azero,Cristina T. Andrade

doi:10.1590/s0103-50532006000500005

Abstract

The galactomannan from Prosopis juliflora (PJ galactomannan) was extracted from milled seeds in water at 50 ºC. 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 13C-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<FONT FACE=Symbol>¢</FONT>) 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 kappa-carrageenan alone. Self-supporting gels obtained by mixing kappa-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.

Highlights

Galactomannans are non-gelling polysaccharides, commercially important mainly for their thickening properties
Food and technological applications have encouraged investigations on mixed systems, those consisting of xanthan gum and locust bean gum (LBG), the galactomannan from Ceratonia siliqua seeds with a high mannose to galactose (M/G) (~4:1) and non-regular D-galactose distribution.[1]
No synergic effect was observed in the viscoelastic behaviour of κ-carrageenan/Prosopis juliflora seeds (PJ) galactomannan in 0.1 mol L-1 KCl at 1.0 g L-1 total polymer concentration

Summary

Introduction

Galactomannans are non-gelling polysaccharides, commercially important mainly for their thickening properties. Compared to κ-carrageenan or agarose gels at the same concentration, the mixed gels with LBG present increased gel strength and elasticity, and a reduced tendency toward syneresis.[2,5,6] Such synergic interactions observed with LBG were found to decrease in magnitude when other galactomannans with higher galactose contents were considered.[2] experimental data have shown that guar gum (GG), the galactomannan from Cyamopsis tetragonolobus seeds with a M/G of approximately 2:1, is effective in producing an increase in viscosity when blended with xanthan gum.[3,7,8,9] Viscoelastic measurements of xanthan gum mixtures with GG samples of different molecular weights showed a significant effect of molecular weight; the higher the molecular weight, the stronger the effect.[10] At high extents of enzymatic modification, GG was shown to interact synergically with xanthan to produce gels with elastic modulus and yield stress similar to or exceeding those of locust bean gum.[11] In mixtures with κ-carrageenan[12] and agarose,[13] GG was found to play a role in the gelation process of the mixed systems. A sample of κ-carrageenan, with intrinsic viscosity of 9.68 dL g-1 in 0.1 mol L-1 NaCl at 25 oC and 24.5% (m/m) sulfate content, was obtained as sodium salt from Hypnea musciformis, according to the procedure described elsewhere.[16]

Extraction procedures

Results and Discussion

Conclusions