Gum arabic is an electrostatically-charged polysaccharide with well-established uses as an emulsifier and thickening agent in the food and beverage industries. What is less known, however, is that high concentration suspensions of the gum will form gels when exposed to iron(III) ions, but not iron(II) or even other trivalent cations. To our knowledge, this gelation is unreported in chemical literature and was only discovered in the late 20<sup>th</sup> century as part of an alternative photography technique. This study uses a staged approach to understanding the phenomenon, starting with the characterization of the suspension at low gum concentrations. Light scattering techniques showed changes in the conformation and size of these gum arabic colloids, and UV-Vis spectroscopy has given evidence of iron(III) complexation. As the gum concentration was increased to the gel transition point, infrared spectroscopy was used to show that this complexation is a result of carboxylate groups in the gum binding to the iron ions. Finally, we examined the swelling properties of the resulting hydrogel under varying pH values and ionic concentrations. Our results provide the first known characterization of this phenomenon as well as an insight into the material’s applications as a biopolymer-based hydrogel.

Understanding the iron(III)-induced sol-gel transition of gum arabic suspensions

2019 Spring National Meeting

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