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Measurements of Singlet Oxygen‐Quenching Activity of Vitamin E Homologs and Palm Oil and Soybean Extracts in a Micellar Solution
Author(s) -
Mukai Kazuo,
Ishikawa Eri,
Ouchi Aya,
Nagaoka Shinichi,
Abe Koichi,
Suzuki Tomomi,
Izumisawa Katsuhiro
Publication year - 2018
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1002/lipd.12053
Subject(s) - singlet oxygen , chemistry , quenching (fluorescence) , reaction rate constant , micellar solutions , aqueous solution , chloroform , absorption (acoustics) , soybean oil , analytical chemistry (journal) , oxygen , organic chemistry , micelle , kinetics , fluorescence , materials science , physics , food science , quantum mechanics , composite material
Recently, a new assay method that can quantify the singlet oxygen‐absorption capacity (SOAC) of antioxidants (AO) and food extracts in homogeneous organic solvents has been proposed. In the present study, second‐order rate constants ( k Q ) for the reaction of singlet oxygen ( 1 O 2 ) with vitamin E homologs (α‐, β‐, γ‐, and δ‐tocopherols [Toc] and α‐, β‐, γ‐, and δ‐tocotrienols [Toc‐3]) were measured in an aqueous Triton X‐100 (5.0 wt%) micellar solution (pH 7.4). Toc‐3 showed k Q values larger than those of Toc in a micellar solution, although Toc and Toc‐3 showed the same k Q values in a homogeneous solution. Similar measurements were performed for 5 palm oil extracts 1–5 and one soybean extract 6, which contained different concentrations of Toc, Toc‐3, and carotenoids. It has been clarified that the 1 O 2 ‐quenching rates ( k Q ) (that is, the relative SOAC value) obtained for extracts 3–6 may be explained as the sum of the productΣ k Q AO ‐ iAO ‐ i / 100of the rate constant ( k Q AO ‐ i ) and the concentration ([AO‐ i ]/100) of AO‐ i contained. The UV–vis absorption spectra of Toc and Toc‐3 were measured in a micellar solution and chloroform. The results obtained demonstrated that the k Q values of AO in homogeneous and heterogeneous solutions vary notably depending on (1) polarity (dielectric constant [ ε ]) of the reaction field between 1 O 2 and AO, (2) the local concentration of AO, and (3) the mobility of AO in solution. The results suggest that the SOAC method is applicable to the measurement of 1 O 2 ‐quenching activity of general food extracts in a heterogeneous micellar solution.