Cercidium praecox brea gum arabinoglucuronoxylans: A viscosant substitute for gum Arabic?

Abstract

Brea gum, obtained from the cuts made in the trunk and branches of Cercidium praecox tree, has been traditionally collected and used as a substitute of gum Arabic (GA) in some regions of Argentina. The rheological performance of purified brea gum (BG) in water (20 °C) was thoroughly evaluated between 1 and 35% w/v. As we previously determined, BG is composed of highly branched arabinoglucuronoxylans (1:0.44:0.16:0.22 xylose:arabinose:glucuronic acid:4-O-methylglucuronic acid molar ratio) with 2.6% of acetyl groups bound to the O-3 of the xylan backbone. The deacetylated form (DBG) was also assayed at 10% w/v. Commercial GA was also considered for comparison. In flow assays (viscosity versus shear rate), BG (1–35%) showed pseudoplastic behavior, and higher initial thickening at very low shear rates (Newtonian viscosity, η0 ≈ 27.3–130 Pa⋅s) than 1–35% w/v GA (η0 ≈ 10–20 Pa⋅s), and 10% DBG (η0 ≈ 7 Pa⋅s). Dynamic mechanical spectra showed “solutions” for GA, and “weak-gel” type networks for BG, more frequency dependent at 35%, probably due to the lowest electrostatic repulsion at pH 3.77. Instead, 10% DBG showed a “dilute solution” spectrum. Heating and cooling ramps (5 °C/min) revealed a gelling temperature for 17.5% (24.2 °C) BG, but not for GA and DBG solutions. BG “weak-gels” were thermo-reversible. Thermal study revealed hydrophobic interactions between BG macromolecules, and hydrogen bonding between DBG macromolecules. BG macromolecules can have an extended hydrophobic (acetylated) side, absent in DBG. Like GA, rheological functionality can yield a commercial use of BG as food additive.