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Frying is a sim­ple cook­ing method used in home and restau­rant meal prepa­ra­tion world­wide. There are two types of fry­ing, shal­low fry­ing and deep fry­ing. Deep fry­ing results in com­plete food immer­sion in fat. While shal­low fry­ing is a par­tial immer­sion of foods in a selected fat. Shallow fry­ing is gen­er­ally seen as the health­ier option.

Extra vir­gin olive oil (EVOO) is a health­ier choice of cook­ing oil for use in either of these fry­ing meth­ods. A recent study, pub­lished in Food Research International, aimed to estab­lish how fry­ing fish not only affected the lipids (fats) in the fish but also how the cook­ing oil changed dur­ing the shal­low-fry­ing process.
See more: Dispelling the Myths of Frying with Olive Oil
The study looked at two dif­fer­ent types of super­mar­ket-bought oils, EVOO and sun­flower oil. Both oils and fish sam­ples were sub­mit­ted to two dif­fer­ent shal­low-fry­ing con­di­tions, a house­hold microwave in a domes­tic ceramic bak­ing dish oper­at­ing at 900W; and in a domes­tic pan over elec­tric heat.

The oils were first fried in the absence of food and the lipid results extracted. New oil sam­ples were then used to fry fish fil­lets under the con­di­tions out­lined above, in the microwave and in a pan. Domestic tem­per­a­tures were mim­ic­ked for the exper­i­ments with an oil tem­per­a­ture of 170°C (340°F) and a cook­ing time of 2.5 min­utes for each fil­let side.

Specifically, the fish sam­ples were farmed gilt­head sea bream and farmed European sea bass. The fish were pre­pared, gut­ted, cleaned and fil­leted into roughly 300 g pieces and were of sim­i­lar dimen­sions in terms of width and length. Lipid extracts were taken from each fried fish sam­ple. There was also fat extracted from one raw sam­ple, act­ing as the con­trol sam­ple.

The results of the study showed that over­all EVOO is a more sta­ble cook­ing oil than sun­flower oil for fry­ing fish.

Regardless of the oil used, there is a lipid migra­tion that occurs between the fish and the culi­nary oil selected for cook­ing. For instance, EVOO oil sam­ples were richer in omega 3 and sat­u­rated fats after fry­ing, and lower in oleic groups. The over­all fat con­tent of the fish dropped in all sam­ples, from 26 to 43 g before fry­ing to 24 to 28 g after. The results showed there was a 19 to 28 per­cent migra­tion of fish lipids across to the fried oils.

The exchange occurs the other way as well. The type of lipids con­tained in each oil migrate to inte­grate with the fish lipids dur­ing cook­ing. For instance, fish becomes richer in oleic polyphe­nols when cooked with EVOO. The results show­ing a 15- to 25-per­cent migra­tion of oil frac­tions migrated over to the fish fil­lets from culi­nary oils.

As expected, the sun­flower oil had a smaller resis­tance to oxi­da­tion and degra­da­tion than EVOO. Frying or heat­ing in the microwave causes less oil oxi­da­tion and degra­da­tion than pan fry­ing. However, accord­ing to the study, no thermo-oxi­da­tion was found in EVOO. The high­est oxi­da­tion com­pounds were found in the sun­flower pan-fried sea bass.

The authors con­cluded that, ​“the selec­tion of the cook­ing oil is of para­mount impor­tance due to its impact on the fish lipid pro­file and on the pos­si­ble gen­er­a­tion of toxic com­pounds in the oil dur­ing fry­ing, which can have a great influ­ence on food safety and human health.”

And it appears from their results, EVOO is the bet­ter option of the two.

• Food Research International