Details

Autor(en) / Beteiligte

• Pastoriza-Gallego, María José
• Losada-Barreiro, Sonia
• Bravo-Díaz, Carlos

Titel

Effects of acidity and emulsifier concentration on the distribution of vitamin C in a model food emulsion

Ist Teil von

• Journal of physical organic chemistry, 2012-11, Vol.25 (11), p.908-915

Ort / Verlag

Bognor Regis: Blackwell Publishing Ltd

Erscheinungsjahr

2012

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• We have analyzed the effects of acidity and emulsifier concentration on the distribution of ascorbic acid or vitamin C (VC) in a model emulsion prepared by mixing octane, acidic (HCl) water and the non‐ionic surfactant hexaethyleneglycol monododecyl ether (C12E6). VC is oil insoluble, and only the partition constant between the interfacial and aqueous regions (PWI) is needed to describe its distribution within the emulsion. The PWI values are calculated from the kinetic analyses of the variation of the observed rate constant (kobs) determined electrochemically for the reaction between the hydrophobic 4‐hexadecylbenzenediazonium (16‐ArN2+) ions and VC with the emulsifier concentration. The determined PWI values (PWI = 4–25) are low in comparison with those obtained for more hydrophobic antioxidants like vitamin E, and pH dependent, decreasing upon decreasing the acidity of the medium. These low values are reflected in the distribution of VC so that a large fraction (70%) is located in the aqueous region at low emulsifier concentrations. At a given pH, the %VC in the aqueous region decreases upon increasing the emulsifier concentration; meanwhile, at a given emulsifier concentration %VC increases upon lowering the acidity. The intrinsic rate constants in the interfacial region kI for the reaction between 16‐ArN2+ and VC have also been determined at different acidities. Their variation with the pH follows an upward bend curve, suggesting an inverse dependence of kI with the acidity of the medium, in keeping with the proposed mechanism for the reaction. The results may be of some interest to the food and pharmaceutical industries because of the extensive use of VC as antioxidant or preservative and because of the health benefits of VC. Copyright © 2012 John Wiley & Sons, Ltd. The distribution of ascorbic acid (vitamin C [VC]) in an emulsion composed of octane, acidic water and the non‐ionic surfactant hexaethyleneglycol monododecyl ether (C12E6) has been determined by employing a kinetic method that exploits the reaction between a hydrophobic arenediazonium, 16‐ArN2+ and VC. The fraction of VC in the interfacial region increases upon increasing the surfactant volume fraction and on increasing the acidity of the medium.