title: Origin and thermodynamic properties of the instability of synthetic azo colorants in gum arabic solutions.
abstract: The instability of some industrially important synthetic azo colorants, including sunset yellow, azorubine, and allura red, toward gum arabic in aqueous solution has been a long-standing problem for the beverage and confectionery industries. Precipitation of these colorants causes the deterioration of product appearance and properties. This work examines the origin and nature of the problem by analysis of the precipitate and thermodynamic studies of gum arabic-colorant interactions using isothermal titration calorimetry (ITC). The presence of divalent alkaline earth metals in gum arabic samples, that is, calcium and magnesium, is shown to be responsible for the precipitation of the azo colorants. There is no direct interaction between gum arabic and the colorant molecules, and the precipitate is formed likely due to the mediation/bridging by the divalent cations. The thermodynamic knowledge gained from the ITC studies, for example, binding affinity, stoichiometry, and enthalpy, enables interpretation of many industrial observations.
authors.affiliation: Glyn O. Phillips Hydrocolloid Research Center, North East Wales Institute, Plas Coch, Mold Road, Wrexham LL11 2AW, United Kingdom. y.fang@newi.ac.uk
authors.forename: Yapeng
authors.initials: Y
authors.lastname: Fang
authors.forename: Saphwan
authors.initials: S
authors.lastname: Al-Assaf
authors.forename: Makoto
authors.initials: M
authors.lastname: Sakata
authors.forename: Glyn O
authors.initials: GO
authors.lastname: Phillips
authors.forename: Matthias
authors.initials: M
authors.lastname: Schultz
authors.forename: Vivianne
authors.initials: V
authors.lastname: Monnier
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D011232:Chemical Precipitation; D004355:Drug Stability; D005505:Food Coloring Agents / Q000737:chemistry*; D006170:Gum Arabic / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D001391:Azo Compounds; D005505:Food Coloring Agents; D006170:Gum Arabic