Structural characteristics and rheological properties of locust bean galactomannans: a comparison of samples from different carob tree populations

Abstract

Water-soluble galactomannans were isolated from the seeds of 12 carob tree populations grown in different regions of southern Greece. Their structures, molecular weight distributions and rheological properties were examined. The intrinsic viscosity values and estimated average molecular weights varied in the ranges 8.15±13.02 dl g À1 and (2.3±3.9) Â 10 6 respectively. Molecular sieve chromatography showed large variations in the molecular size distributions. The Manp/Galp ratio varied between 3.08 and 3.82, as determined by GC analysis of the alditol acetate derivatives of the monomeric constituents. There were also differences in the relative distribution of the free (ManpManp), monosubstituted (Manp-Manp(Galp)) and disubstituted (Manp(Galp)-Manp(Galp)) dyads of b-(1→4)-mannose, as revealed by 13 C NMR spectroscopy of the native polysaccharides. The pseudoplastic behaviour of galactomannan solutions (10±20 g l À1) was con®rmed by steady shear and dynamic rheological tests. Aqueous galactomannan (5 g l À1 )±xanthan gum (5 g l À1 ) mixed systems gave gels on cooling (G' ) G@). Galactomannans with high limiting viscosities, high Manp/Galp ratios and a low proportion of the Manp(Galp)-Manp(Galp) dyad yielded the strongest mixed gel network structures with xanthan, implying that interchain associations between the two polymers occur via the unsubstituted segments (`smooth regions') of the carob galactomannan chains.

Isolation and rheological characterization of Mucuna flagellipes seed gum

“…Application of the Mark-Houwink equation gave a viscosity average molecular mass of 2.1 x 10 6 which is similar to the viscosity average molecular mass values reported for other galactomannans such as carob gum (Lazaridou et al, 2000). polysaccharides (Morris et al, 1981).…”

Physical and rheological characterization of seeds of three legume trees

“…The gums of honey locust and tara showed the same tendency as the algarrobo gums ( Figure 6); at both concentrations the dispersions of honey locust were less stable than those of tara, and also had lower viscosity. The gum of tara showed the greatest viscosity and stability of all studied gums, which is in agreement with its greater mannose content (Lazaridou et al, 2001).…”

Osmotic Properties of Polysaccharides Solutions

“…The second method uses a combination of extraction and purification [24,25]. Whole brans are subjected to milling and then extracted using water and precipitation with the use of alcohol (ethanol or isopropanol) [26][27][28]. The flour is a non-ionic biopolymer belonging to galactomannans; therefore, the main chain of this polysaccharide is formed by mannose units joined by β-(1,4)-glycosidic linkages, to which single units of D-galactopyranose are attached by the α-(1,6) linkages.…”

“…The ratio of mannose to glucose ranges between 3.1 and 3.9 [31][32][33] and depends on the variety, source and most of all on the applied extraction method [33]. The galactose content of approximately 20% is lower in comparison to other galactomannans, such as guar gum and tara gum [28,34]. The ratio of mannose to galactose (M/G) has impact on this polysaccharides solubility in water [31,35], the higher ratio of (M/G) results in better thickening properties [35].…”