Influence of structural properties of emulsifiers on citral degradation in model emulsions

Abstract

The storage stability of compounds encapsulated in emulsions is strongly influenced by the properties of the droplet interfacial membrane. To evaluate the effect of emulsion droplet interface thickness on the degradation of citral, emulsions were prepared using polyoxyethylene alkyl ether-type emulsifiers with hydrophilic and hydrophobic groups of various sizes. Acid cyclization of citral at pH 3 promoted faster degradation than that at pH 7. Ferrous irons accelerated citral degradation in the emulsions at pH 3 but not at pH 7, because they decomposed the products of the acid-catalyzed cyclization of citral through redox reactions rather than direct degradation. Water-soluble radicals dramatically increased the rate of citral degradation, irrespective of pH. Notably, at low pH, the rate of citral degradation by ferrous irons was higher than that by radicals. These findings suggest that the thickness and density of emulsion droplet surfaces are not important factors for inhibiting citral degradation in emulsions.

Keywords: Citral; Degradation; Emulsions; Interfacial characteristics; Interfacial membrane.

Fig. 1

Time-dependent change in citral concentration in emulsions prepared at 1× (A, B) and 3× (C, D) the MEC at pH 7 (A, C) or 3 (B, D) stored 25 °C

Fig. 2

Effect of ferrous iron (Fe²⁺) on citral decomposition in emulsions prepared at 1× (A, B) and 3× (C, D) the MEC at pH 7 (A, C) or 3 (B, D) stored 25 °C

Fig. 3

Effect of radicals on citral decomposition in emulsions prepared at 1× (A, B) and 3× (C, D) the MEC at pH 7 (A, C) or 3 (B, D) stored 25 °C