Abstract
Superficially similar carbohydrate polymers from similar sources can have dramatically different characteristics. This work seeks to examine the molecular properties responsible for these differences. Protons responsible for cross-polarization in the anomeric region of Acacia nilotica (AN) were replaced easily by deuterium, but not for Acacia modesta (AM). Time constants describing the mobility and cross-polarization transfer were both found to be lower for AM. Variable contact time experiments showed poorer fits and more heterogeneity for AN. Solution state HSQC experiments showed a lower number of environments in the anomeric region for AM. The relaxation time T2 of AM solutions had a lower value consistent with a higher viscosity. The Tg′ of solutions were −14.5°C AN and −18.5°C AM. These results form a largely self-consistent picture of molecular differences between AN and AM, suggesting a more compact but heterogeneous structure for AN and more branching in the case of AM.
Highlights
Gum acacia, known as gum Arabic (E number E 414), is an edible polysaccharide used in the food, pharmaceutical, cosmetic and textile industries, as an emulsifying, suspending and stabilizing agent
A magnified trace shows the superimposed anomeric regions with the complete spectra shown as separate inserts
Acacia nilotica (AN) was more heterogeneous at a chemical level but had a more compact structure in contrast to the more branched structure of Acacia modesta (AM)
Summary
Known as gum Arabic (E number E 414), is an edible polysaccharide used in the food, pharmaceutical, cosmetic and textile industries, as an emulsifying, suspending and stabilizing agent. Grein et al (2013) studied the emulsifying properities of a commercial gum Arabic as well as Acacia mearnsii de Wild gum and concluded that these were dependent on the structure of the polysaccharide, such as the degree of branching, as well as the protein content and molecular weight of the carbohydrate/protein complexes. These authors noticed a difference in the number of anomeric environments as measured by 2D NMR between the two gums. The hypothesis underpinning this research is that information from a series of techniques including NMR, when considered together can provide useful information concerning structural differences between carbohydrate gums
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