Effect of cooking method on the formation of 7-ketocholesterol in Atlantic hake (Merluccius hubbsi) and smooth weakfish (Cynoscion leiarchus) fillets

The levels of cholesterol and 7-ketocholesterol were measured in raw Atlantic hake (Merluccius hubbsi) and smooth weakfish (Cynoscion leiarchus) fillets and in fillets subjected to the following cooking methods: baking in an electric or microwave oven; baking, grilling or stewing in a steam-convection oven; simmering on a stove; electric grilling; and deep frying. The raw samples from both fishes exhibited significantly (p < 0.05) higher cholesterol levels (62.71 ± 6.06 mg/100 g-74.16 ± 3.96 mg/100 g) than the processed fillets. In all of the samples, 7-ketocholesterol was detected at significantly (p < 0.05) different levels depending on the cooking method and the type of fish. Steam cooking keeping the surface of the product moist produced small decrease in the cholesterol content (26.65%-29.96%) and a low level of 7-ketocholesterol in the samples (6.90 ± 0.21 μg/g-6.47 ± 0.28 μg/g). Baking in electric or steam-convection ovens at high temperatures and long times greatly reduced the cholesterol content (52.77%-65.08%), which was associated with a large increase in 7-ketocholesterol levels (11.54 ± 0.45 μg/g-13.94 ± 1.17 μg/g). These results indicate the necessity of revising the baking procedures for fish to increase the healthiness of food.