Influence of the hydrophilic head size and hydrophobic tail length of surfactants on the ability of micelles to stabilize citral

BACKGROUND: Surfactant-made micelles can control the rate of chemical degradation of poorly water-soluble food flavors. To evaluate how the molecular structure of surfactant has an influence on the chemical decomposition rate of citral, micelles were prepared with polyoxyethylene alkyl ether-type surfactants that had similar molecular structures but various hydrophilic head sizes and hydrophobic tail lengths. RESULTS: At a critical 20x micelle concentration of surfactant, there was no significant difference in the chemical degradation rate of citral in micelles in neutralpH, regardlessof thehydrophilic head size orhydrophobic tail length. In an acidic environment, the degradation rate constant of citral generally increased proportionally with increasing hydrophilic head size of surfactant (0.1563 and 0.2217 for surfactants with 23 and 100 oxyethylene units, respectively) but the length of hydrophobic tail did not affect the citral stability. Also, little difference (0.2217 and 0.2265 for surfactant having 100 oxyethylene units with and without Fe3+) in degradation rate constant of citral between simple micellar solution and micellar solution containing iron suggested that iron ions could not accelerate citral degradation in micelles, regardless of the form of iron (Fe2+ and Fe3+). CONCLUSION: This work concludes that although the concentration of surfactant could be relevant, if its concentration could be controlled in the samemanner as the critical micelle concentration, then a polyethylene alkyl ether-type surfactantwith a small hydrophilic head couldmore efficiently stabilize citral at an acidic pH. (C) 2015 Society of Chemical Industry