45C-24 |
Photooxidation and photosensitized oxidation of linoleic acid |
J. H. LEE and D. B. MIN. Dept. of Food Science & Technology, Ohio State Univ., 2015 Fyffe Ct., 110 Parker Food Science Bldg., Columbus, OH 43210-1007 Light-induced lipid oxidation has been studied on unsaturated fatty acids and vegetable oils with or without addition of photosensitizers. However, the effects of photooxidation and chlorophyll photosensitized oxidation on the formation of volatile compounds from linoleic acid and the formation mechanisms of light-induced volatiles were not fully understood. The objectives of this work were to study the effects of light and chlorophyll on the formation of volatile compounds from linoleic acid model system and to propose the formation of volatiles by photosensitized oxidation. Samples of 0.10 g linoleic acid with or without added 5 ppm chlorophyll were put in 10-mL serum vials and sealed air-tight with Teflon-coated rubber septa and aluminum caps. Sample bottles were kept at 4 oC in a fluorescent light box. Volatile compounds of sample bottles were isolated at 0, 6, 12, 24, and 48 hr by solid phase microextraction method and identified by gas chromatography-mass spectrometry. Sample bottles were prepared in duplicate at each sample analysis. Total volatile compounds in linoleic acid without added chlorophyll under light and in the dark did not increase and the same for 48 hr at 4 oC. Total volatile compounds in linoleic acid with added 5 ppm chlorophyll under light at 4 oC for 0, 6, 12, 24, and 48 hr, increased from 8.9 to 11.6, 21.7, 26.1, 29.3 (104) in electronic counts, respectively. 2-Pentylfuran, an undesirable reversion flavor compound in soybean oil, 2-octene-1-ol, 2-heptenal and 1-octene-3-ol were formed by photosensitized oxidation only. Light excited photosensitizers like chlorophyll can generate singlet oxygen from ordinary triplet oxygen. 2-Pentylfuran, 2-heptenal, and 1-octene-3-ol can come from C10, C12, and C10 hydroperoxide of linoleic acid, respectively, which can be formed by singlet oxygen oxidation but not by triplet oxygen oxidation on linoleic acid. Photosensitizers like chlorophyll play important roles in the formation of volatile compounds. Singlet oxygen oxidation is mainly responsible for the formation of 2-pentylfuran, 2-heptenal, 1-octene-3-ol, and 2-octene-1-ol in photosensitized oxidation of linoleic acid.
Session 45C, Food Chemistry: Flavor and aroma chemistry
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