Effects of quenching mechanisms of carotenoids on the photosensitized oxidation of soybean oil

The effects of 0, 1.0 × 10”−5, 2.5 × 10−5, and 5.0 × 10−5 M β‐apo‐8'‐carotenal, β‐carotene, and canthaxanthin on the photooxidation of soybean oil in methylene chloride containing 3.3 × 10−9 M chlorophyll b were studied by measuring peroxide values and conjugated diene content. β‐Apo‐8'‐carotenal, β‐carotene, and canthaxanthin contain 10,11, and 13 conjugated double bonds, respectively. The peroxide values and conjugated diene contents of oils containing the carotenoids were significantly lower (P<0.05) than those of control oil containing no carotenoid. As the number of conjugated double bonds of the carotenoids increased, the peroxide values of soybean oils decreased significantly (P<0.05). The quenching mechanisms and kinetics of the carotenoids in the photosensitized oxidation of soybean oil were studied by measuring peroxide values. The steady‐state kinetics study showed that carotenoids quenched singlet oxygen to reduce chlorophyll‐sensitized photooxidation of soybean oil. The singlet‐oxygen quenching rate constants ofβ‐ apo‐8'‐carotenal, β‐carotene, and canthaxanthin were 3.06 × 109, 4.60 × 109, and 1.12 × 1010 M−1sec−1, respectively.