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Direct Analysis of Lipophilic Antioxidants of Olive Oils Using Bicontinuous Microemulsions

Kuraya, Eisuke, Nagatomo, Shota, Sakata, Kouhei, Kato, Dai, Niwa, Osamu, Nishimi, Taisei, Kunitake, Masashi
Analytical chemistry 2016 v.88 no.2 pp. 1202-1209
alpha-tocopherol, antioxidants, electrochemistry, electrodes, hydrophilicity, hydrophobicity, indium, monitoring, olive oil, oxides, oxygen radical absorbance capacity, phenolic compounds, quantitative analysis, surfactants, toluene
Quantitative analyses of olive oil for lipophilic antioxidants, such as α-tocopherol and phenolics, by simple electrochemical measurements were conducted in a bicontinuous microemulsion (BME), which was bicontinuously composed of saline and toluene microphases with a surfactant system. Lipophilic antioxidants in oils were directly monitored in BME solutions using a lipophilic, fluorinated nanocarbon-film electrode (F–ECR). The combination of a well-balanced BME and extremely biased electrodes, such as strongly hydrophilic indium/tin oxide and strongly lipophilic (hydrophobic) F–ECR, allowed individual monitoring of hydrophilic and lipophilic antioxidants in the same BME solution without any required extraction. Furthermore, values for the charge Q, integrated from observed currents, showed good linear relationships with the results of conventional assays for antioxidant activity, namely, total phenolics and oxygen radical absorbance capacity assays, even with practical food samples. This proposed methodology provided a very simple, rapid, easily serviceable, and highly reproducible analysis that possesses great potential for applications to a wide range of chemical mixtures, in terms of analyte and media, beyond food oils.