Measurements of Singlet Oxygen‐Quenching Activity of Vitamin E Homologs and Palm Oil and Soybean Extracts in a Micellar Solution

• Published in: Lipids Vol. 53; no. 6; pp. 601 - 613
• Main Authors: Mukai, Kazuo, Ishikawa, Eri, Ouchi, Aya, Nagaoka, Shin‐ichi, Abe, Koichi, Suzuki, Tomomi, Izumisawa, Katsuhiro
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.06.2018
• Subjects: Glycine max - chemistry; Kinetic study; Micelles; Molecular Structure; Palm Oil - chemistry; Palm oil extracts; Plant Extracts - chemistry; Quenching reaction; Singlet oxygen; Singlet Oxygen - analysis; Singlet Oxygen - chemistry; SOAC value; Solutions; Vitamin E - chemistry; Vitamin E homologs; Kinetic study; Vitamin E homologs; Singlet oxygen; Quenching reaction; SOAC value; Palm oil extracts
• ISSN: 0024-4201; 1558-9307
• DOI: 10.1002/lipd.12053

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 (kQ) for the reaction of singlet oxygen (1O2) 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 kQ values larger than those of Toc in a micellar solution, although Toc and Toc‐3 showed the same kQ 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 1O2‐quenching rates (kQ) (that is, the relative SOAC value) obtained for extracts 3–6 may be explained as the sum of the product ΣkQAO‐iAO‐i/100 of the rate constant (kQAO‐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 kQ values of AO in homogeneous and heterogeneous solutions vary notably depending on (1) polarity (dielectric constant [ε]) of the reaction field between 1O2 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 1O2‐quenching activity of general food extracts in a heterogeneous micellar solution.