EFFECTS OF QUENCHING MECHANISMS OF CAROTENOIDS ON THE PHOTOSENSITIZED OXIDATION OF SOYBEAN OIL

The effects of 0, 1.0 x 10(-5), 2.5 x 10(-5), and 5.0 x 10(-5) M beta-apo-8'-carotenal, beta-carotene, and canthaxanthin on the photooxidation of soybean oil in methylene chloride containing 3.3 x 10(-9) M chlorophyll b were studied by measuring peroxide values and conjugated diene content. Beta-Apo-8'-carotenal, beta-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 of beta-apo-8'-carotenal, beta-carotene, and canthaxanthin were 3.06 x 10(9), 4.60 x 10(9), and 1.12 x 10(10) M-1sec-1, respectively.