CHEMISTRY OF SINGLET OXYGEN OXIDATION OF FOODS

The effects of beta-apo-8'-carotenal, beta-carotene, and canthaxanthin as well as alpha-, gamma-, and delta-tocopherols on the chlorophyll photosensitized oxidation of soybean oil were studied by measuring peroxides, headspace oxygen, and conjugated diene content. As the number of conjugated double bonds of carotenoids increased, the antioxidant effects of carotenoids increased. alpha-Tocopherol showed the highest antioxidant effect, gamma-tocopherol second, and then delta-tocopberol. Quenching mechanisms indicated that carotenoids and tocopherols quenched singlet oxygen to act as antioxidants in the chlorophyll photosensitized oxidation of soybean oil. The singlet oxygen quenching rate constants of beta-apo-8'-carotenal, beta-carotene, and canthaxanthin were 3.06 x 10(9), 4.6 x 10(9) and 1.12 x 10(10) M(-1)S(-1), respectively. The quenching rate constants of a-tocopherol were 2.7 x 10(7) M(-1)S(-1) by peroxide value and 2.6 x 10(7) M(-1)S(-1) by headspace oxygen.