Cholesterol photooxidation as affected by combination of riboflavin and fatty acid methyl esters

The effect of combination of riboflavin and fatty acid methyl esters on cholesterol photooxidation was studied. Samples containing both riboflavin and fatty acid methyl esters were exposed to light as 25 °C for 28 days. The various cholesterol oxidation products (COPs) were analyzed by gas chromatography–mass spectrometry (GC–MS), while riboflavin was determined by high-performance liquid chromatography (HPLC). Results showed that both riboflavin and fatty acid methyl esters could promote COPs formation and cholesterol degradation, and the degradation fits a first-order model. Riboflavin had a more pronounced effect than fatty acid methyl esters. 7-Keto was generated in highest amount, followed by 5,6β-EP, 3,5- cholestadien-7-one, 5,6α-EP, 7α-OH and 7β-OH. The formation of 3,5-cholestadien-7-one was probably due to dehydration of 7-keto through energy liberated during illumination.