LEVELS AND FORMATION OF OXIDIZED CHOLESTEROLS IN PROCESSED MARINE FOODS

The contents of oxidized cholesterols in uncooked and processed marine products (air-dried sardine, air-dried squid, canned squid, and pickled and spiced Alaskan pollack roe) were measured. Raw fish contained essentially no oxidized cholesterols, while the processed products examined contained 11.0-28.7 mg/100 g of oxidized cholesterols, and 7alpha-hydroxycholesterol (2.7-3.8 mg/100 g), 7beta-hydroxy-cholesterol (2.8-9.8 mg/100 g), 5alpha-epoxycholesterol (0.2-5.8 mg/100 g), 5beta-epoxycholesterol (0.7-4.9 mg/100 g), and 7-ketocholesterol (1.9-5.3 mg/100 g) were detected. To know the interaction of lipid oxidation with cholesterol oxidation, cholesterol was heated with or without various fats (tristearin, beef tallow, triolein, soybean oil, safflower oil, linseed oil, and sardine oil) at 100-degrees-C for up to 24 h. Cholesterol was stable, and essentially no oxidized cholesterol was produced when it was heated alone. However, when fats were present simultaneously, cholesterol was unstable, in particular when heated with unsaturated fats; the content of cholesterol was readily reduced, and oxidized cholesterols were generated shortly after heating. The observations indicated that lipid peroxidation precedes cholesterol oxidation.