UPV/EHU University of the Basque Country researchers have shown that the choice of cooking oil is hugely important. Οwing to its impact on the fish lipid profile and on the possible generation of toxic compounds in the oil during frying can influence food safety and human health.
The journal Food Research International has published the article Studied by H-1 NMR, which deals with the work carried out by Bárbara Nieva-Echevarría, Encarnación Goicoechea, María José Manzanos and María Dolores Guillén. "The influence of frying technique, cooking oil and fish species on the changes occurring in fish lipids and oil during shallow-frying".
Seabass and seabream fillets fried in a pan and in a microwave oven using Extra Virgin Olive Oil and refined Sunflower oil.
Migration of lipid observed during the shallow-frying of the fish under domestic conditions. The fish lipids migrate to the frying oil, and oil's components also transferred to the fish fillet. As a result, the composition of the oil used for frying is modified. Firstly, it is enriched by the acyl groups ('fatty acids') that are present in a higher concentration in the fish fat than in the original oil. Secondly, and it is depleted in the acyl groups present in a higher concentration in the original oil than in the fish fat. So after having been used for frying, the extra virgin olive oil was richer in omega-3, omega-1 acyl groups, linoleic and saturated fats (from the fish) and poorer in oleic, which is the main acyl group in olive oil. Likewise, after having been used for frying, the sunflower oil was richer in all the acyl group types (coming from the fish) except linoleic, which is the majority acyl group in sunflower oil. Furthermore, after frying, both types of oil were enriched by small amounts of cholesterol (from the fish).
The fish lipids migrate to the frying oil, and oil's components also transferred to the fish fillet.
As regards the fat composition in the fish fillets also changed during the frying process. They became enriched by the acyl groups present in a higher concentration in the frying oil than in the fillet and in-plant sterols. Simultaneously, during the frying process, the lipids in the fish fillets were depleted in the acyl groups and minority components present in a higher concentration in the raw fillet than in the original oils. Such as, for example, the omega-3 docosahexaenoic (DHA) and eicosapentaenoic (EPA) polyunsaturated groups.
The healthiest option for frying is to use extra virgin olive and fry in the microwave.
Besides the migration of lipids during frying, because these oils are subject to high temperatures (170 ºC) in the presence of oxygen, inevitable small-scale thermal oxidation may take place in them. In the extra virgin olive oil used for frying fish, this thermal oxidation reaction did not occur as it is more degradation-resistant than sunflower oil. Yet in the sunflower oil used for frying fish in the frying pan, secondary oxidation compounds (aldehydes) were formed; some of them regarded as potentially toxic depending on the concentration in which they found. It is crucial to notice that these compounds did not form in the sunflower oil used to fry the fish in the microwave oven. Therefore, because of the results obtained and bearing in mind the generation of these compounds that are potentially harmful to health, the healthiest option for frying is to use extra virgin olive and fry in the microwave.
The fish species used was also seen to be a factor that considerably influences the fat absorption-desorption process during frying. Seabream's fat content had diminished after frying while that of the Seabass remained similar or increased to the starting level.
This study shows that the frying technique, the type of oil used and the fish species exert a significant influence on the changes that take place during the frying process. Correctly selecting the oil is of paramount importance owing to its impact on the final composition of the fat in the cooked fillet and the possible generation of potentially toxic compounds in the oil during the frying process, which will significantly influence food safety and human health.