Effects of Phosphatidylcholine on Interaction of α‐Tocopherol and β‐Carotene in Photosensitized Oxidation of Emulsions

Abstract

The interaction between a-tocopherol (500 mg/ kg) and b-carotene (10 mg/kg) during chlorophyll-photosensitized oxidation of a sunflower oil emulsion was studied in the presence or absence of phosphatidylcholine (PC, 250 mg/kg) by determining peroxide (POV) and conjugated dienoic acid (CDA) values. Chlorophyll, a-tocopherol, b-carotene, and PC contents in the emulsion were also monitored. a-Tocopherol and b-carotene individually and interactively decreased the POV and CDA values of oil in the emulsion by singlet oxygen quenching. PC decreased the POV and CDA values of oil, however, the values of the emulsion with added a-tocopherol, b-carotene, and PC were not significantly different from those of the emulsion with added a-tocopherol and b-carotene without PC. Contents of a-tocopherol did not change during 24-h oxidation, whereas co-present PC significantly caused a-tocopherol and chlorophyll degradation. b-Carotene and PC contents significantly decreased to 45.5 and 51.3 %, respectively, after 24 h, and a-tocopherol protected b-carotene from degradation. The results suggest that PC had no net effects on the interactive antioxidant activity of a-tocopherol and b-carotene during chlorophyllphotosensitized oxidation of the emulsion through free radical generation, chlorophyll degradation, and lessening the potency of a-tocopherol as a singlet oxygen quencher.