title: Colloidal stability and chemical reactivity of complex colloids containing Fe³⁺.
abstract: The reactivity of iron contained within insoluble colloidal metal-pyrophosphate salts was determined and compared to the reactivity of a soluble iron salt (FeCl3). As a model system for the reactivity of iron in food products, the formation of an iron-polyphenol complex was followed with spectrophotometry. Three types of systems were prepared and their colloidal stability and reactivity studied: Fe(3+) pyrophosphate, protein-coated Fe(3+) pyrophosphate and mixed-metal pyrophosphates containing Fe(3+) and a second cation M. The additional cation used was either monovalent (sodium) or divalent (M(2+)). It was found that: (i) incorporating iron in a colloidal salt reduced its reactivity compared to free Fe(3+) ions; (ii) coating the particles with a layer of hydrophobic protein (zein) increased stability and further decreased the reactivity. Finally, the most surprising result was that (iii) a mixed system containing more Fe(3+) than M actually increased the reactivity of the contained iron, while the reverse, a system containing excess M, inhibited the reactivity completely.
authors.affiliation: Van 't Hoff Laboratory for Physical and Colloidal Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands. Electronic address: Y.M.vanleeuwen@uu.nl.
authors.forename: Y M
authors.initials: YM
authors.lastname: van Leeuwen
authors.affiliation: Unilever R&D Vlaardingen, Olivier van Noortlaan 120, 3133 AT Vlaardingen, The Netherlands; Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
authors.forename: K P
authors.initials: KP
authors.lastname: Velikov
authors.affiliation: Van 't Hoff Laboratory for Physical and Colloidal Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands. Electronic address: W.K.Kegel@uu.nl.
authors.forename: W K
authors.initials: WK
authors.lastname: Kegel
mesh_terms: D003102:Colloids / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*
chemical_list: D003102:Colloids; D005290:Ferric Compounds
keywords: Colloidal salt; Essential minerals; Micronutrients; Reactivity