Formation and inhibition of compounds generated by oxidative reactions in lipids of Nile Tilapia

Abstract

One of the main characteristics of fish lipids is the high content of long chain polyunsaturated fatty acids (PUFA), which are known due to their beneficial health effects. On the other hand, PUFA are highly susceptible to oxidation and can generate trans-4-hydroxy-2-nonenal (HNE) from omega 6 PUFA (PUFA n6) and trans-4-hydroxy-2-hexenal (HHE) from omega 3 PUFA (PUFA n3). The studies that investigate these compounds in food are scarce in the literature, and these compounds need to be studied because they are the most recent markers of lipid oxidation and harmful to health, as well as, to verify which thermal processes will accelerate their formation and means to minimize it. Moreover, fishes, which are food of animal origin, have cholesterol in the composition, which can also undergo oxidation generating cholesterol oxides. The compounds HNE, HHE and cholesterol oxides are considered cytotoxic, mutagenic, carcinogenic and atherogenic, thus, highly prejudicial to public health. One way to delay the lipid oxidation is the addition of antioxidants, for instance, bixin, the main carotenoid of annatto, has proved to have antioxidant capacity. The extraction of lipids is the initial stage for the determination of these compounds and the traditional methods consume a huge amount of solvents which contribute to the environment degradation. Thus, the first aim will be to optimize a method to lipid extraction by microwave assisted extraction (MAE) using less pollutant solvents in small amounts. The second aim will be to verify the formation and inhibition of compounds originated from the oxidation of fish lipids. Samples of Nile tilapia (Sarotherodos niloticus) (cooked at 95ºC for 30 min, grilled at 165ºC for 8 min, baked in electric oven at 180ºC for 10 min and cooked in microwave oven at maximum power for 5 min) will be analyzed. The formation of oxidation compounds due to thermal treatment will be verified by the quantification of content of cholesterol oxides and decomposition compounds of PUFA n6 and n3 (HHE and HNE). In addition, the fatty acid composition, total lipid, moisture and bixin contents will be determined. Initially, the methods to determine total lipids and fatty acids by MAE, cholesterol oxides by GC-MS and the compounds HHE and HNE by HPLC-UV-MS will be optimized. Finally, it will be investigated if there is a correlation between the compounds formed during lipid oxidation. (AU)