EFFECTS, QUENCHING MECHANISMS, AND KINETICS OF CAROTENOIDS IN CHLOROPHYLL-SENSITIZED PHOTOOXIDATION OF SOYBEAN OIL

The effects of 0, 1.75 X 10-5M, 3.50 X 10-5, and 5.25 X 10-5 M lutein, zeaxanthin, lycopene, isozeaxanthin, and astaxanthin which contain 10, 11, 11, 11, and 13 conjugated double bonds, respectively, on the photooxidation of soybean oil containing 4.4 X 10-9 M chlorophyll were studied by measuring peroxide values of the oil. The antioxidant effectiveness of the carotenoids increased as the number of conjugated double bonds of carotenoid increased. The peroxide value of oil containing the carotenoid with 10 conjugated double bonds was significantly higher (P < 0.05) than the oil containing carotenoids with 11 or 13 conjugated double bonds at the concentration of 5.25 X 10-5 M. The quenching mechanisms and kinetics of the above carotenoids in the photooxidation of soybean oil containing 3.3 X 10-9 M chlorophyll were studied by measuring the headspace oxygen depletion of oil bottle using gas chromatography. The carotenoids quenched singlet oxygen to reduce the chlorophyll-sensitized photooxidation of soybean oil. The total singlet oxygen quenching rate constants of lutein, zeaxanthin, lycopene, isozeaxanthin, and astaxanthin were 5.72 X 109, 6.79 X 109, 6.93 X 109, 7.39 X 109, and 9.79 x 109 M-1 s-1, respectively. © 1990, American Chemical Society. All rights reserved.