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Singlet oxygen is formed in foods from triplet oxygen in the presence of light and photosensitizers. Singlet oxygen oxidation of linoleic and linolenic acids produces 2-pentyl furan and 2-pentenyl furan, respectively, which are responsible for undesirable reversion flavor in soybean oil. The reversion flavor makes soybean oil less acceptable to food manufacturers and consumers. Milk stored under light contains sulfur compounds such as methional, dimethyl sulfide, dimethyl disulfide, and methionine sulfoxide, which are thought to be responsible for objectionable sunlight flavor. The sulfur compounds are produced from the singlet oxygen oxidation, and riboflavin acts as a photosensitizer. Rapid destruction of riboflavin, vitamin D, and ascorbic acid in milk stored under light is due to singlet oxygen oxidation. Ascorbic acid is more labile to singlet oxygen oxidation than riboflavin.
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