Is Cooking With Olive Oil Healthy?

Extra vir­gin olive oil (EVOO) is well known as a source of bioavail­able phe­no­lic com­pounds that pro­vide var­i­ous health ben­e­fits across many dis­eases — can­cer, car­dio­vas­cu­lar dis­ease, neu­rode­gen­er­a­tive dis­or­ders and oth­ers.

Olive oil is a monoun­sat­u­rated fat that is higher in bioac­tive com­pounds com­pared to other veg­etable oils. While it is well known to be an all round healthy oil, main­tain­ing the vast array of nutri­tional qual­i­ties under cook­ing processes is often ques­tioned. So let’s eval­u­ate what the research shows sur­round­ing OO and var­i­ous domes­tic cook­ing processes — deep fry­ing, pan fry­ing, boil­ing and roast­ing.

Deep Frying

The most recent study, pub­lished in Food Chemistry, 2015, aimed to study the effects of dif­fer­ent domes­tic cook­ing processes on the phe­no­lic com­po­si­tion of var­i­ous Mediterranean foods, potato, tomato, pump­kin, egg­plant, cooked in EVOO. Four dif­fer­ent cook­ing processes were tested, deep fry­ing (180°C), sautéing (80 – 100°C), boil­ing (plain water), boil­ing (water+EVOO mix­ture — both boil­ing at 100°C). Each was sub­jected to 10 min­utes of cook­ing fol­lowed by five min­utes of cool­ing before refrig­er­a­tion and test­ing.
See Also:Pairing Extra Virgin Olive Oils with Foods
Surprisingly, the results of the study showed that the over­all qual­ity of the veg­eta­bles was sig­nif­i­cantly improved when deep-fried in EVOO because the pro­duce becomes enriched with EVOO phe­nols trans­ferred from the oil. However, though this may be the case, it’s impor­tant to note that the fat con­tent is sig­nif­i­cantly increased com­pared to boil­ing as is to be expected.

It’s also impor­tant to note that results for each veg­etable did vary so while the phe­no­lic com­pounds were found to be higher in the deep-fried veg­eta­bles, the over­all con­clu­sion was that ​“each cooked veg­etable devel­oped spe­cific phe­no­lic and antiox­i­dant activ­ity pro­files result­ing from the char­ac­ter­is­tics of the raw veg­eta­bles and the cook­ing tech­niques.”

Another study, pub­lished in Food Chemistry Toxicology, 2010, aimed to specif­i­cally eval­u­ate the effects of deep fry­ing with OO. Five sam­ples of com­mer­cial OO, includ­ing one EVOO, from the north­east Portugal region were used for the study. Potatoes were used as the veg­etable sub­ject with domes­tic deep-fat elec­tric fry­ers at 170°C. All the OOs had sim­i­lar total phe­no­lic com­pounds (TPC) before fry­ing.

The results showed that, ​“the degra­da­tion rates were sim­i­lar between all olive sam­ples, with a 0.7 per­cent increase per hour in the EVOO, and 0.8 per­cent in all the other olive sam­ples, with­out clear dif­fer­ences.” EVOO obtained the high­est oxida­tive sta­bil­ity. After 6 hours of fry­ing, only the EVOO still con­tained phe­nols, while the other sam­ples were dimin­ished. Still, it is rare to cook for 6 – 12 hours in domes­tic sit­u­a­tions so over­all the study con­cluded that olive oil, inde­pen­dent of the com­mer­cial cat­e­gory cho­sen is ​“clearly resis­tant to degra­da­tion under domes­tic fry­ing con­di­tions (170 °C).”

Another study, pub­lished in the Journal of Agriculture and Food Chemistry, 2003, took potato slices and sub­jected them to deep fry­ing for 10 min­utes at 180°C in EVOO. This study showed that after just one fry­ing process, the phe­no­lic com­pounds reduced by 40 – 50 per­cent com­pared to their orig­i­nal con­cen­tra­tion. And after 6 fry­ing ses­sions, less than 10 per­cent of the orig­i­nal con­cen­tra­tions remained. The total antiox­i­dant capac­ity reduced from 740 umol of Trolox/kg down to less than 250 umol after the first fry­ing ses­sion and fur­ther down to 139 – 144 umol/kg after 12 fry­ing ses­sions. In regards to the for­ma­tion of polar com­pounds and total polar mate­r­ial, EVOO showed good resis­tance.

Pan-Frying

Interestingly, pan fry­ing results in slightly faster degra­da­tion of EVOO com­pared to deep fry­ing. Authors of a review, pub­lished in Food Research International, 2013, sug­gest that this is likely due to ​“higher food: oil con­tact sur­face, higher expo­sure to atmos­pheric oxy­gen, and lower tem­per­a­tures under pro­cess­ing.” However, they also note that ​“in com­par­i­son with other veg­etable oils, the fried food is enriched with olive oil antiox­i­dants, as long as the olive oil is not exten­sively heated.”

Boiling

A study, pub­lished in Food Science and Technology, 2010, used a sam­ple of EVOO and OO with car­rots, onions, and pota­toes, to eval­u­ate the effect of boil­ing. Vegetables were boiled for 60 min­utes with 60 g of each OO added at the begin­ning or 15 min­utes before the end of the boil­ing process. As expected, the results showed that boil­ing does not result in oxi­da­tion. Tocopherols and all polyphe­no­lic com­po­nents decreased in con­cen­tra­tion. However, adding OO to the boil­ing process just 15 min­utes before the end of the boil­ing process increased ​“con­tent of both oleano­lic acid deriv­a­tives, 3,4‑DHPEA-EA and 4- HPEA-EA, and hydrox­y­ty­rosol acetate.”

Roasting

A study, pub­lished in Food Chemistry, 2010, looked at the behav­iour of olive oil phe­no­lic com­pounds dur­ing roast pro­cess­ing. According to the study, ​“Samples included extra-vir­gin olive oil (EVOO), vir­gin olive oil (VOO), olive oil (OO), sun­flower oil (SFO), soy oil (SO), corn oil (CO) and peanut oil (PNO). Beef (150 g, cube shape) or 150 g of pota­toes (six quar­ters of pota­toes).” The veg­eta­bles were processed in 60 g of each oil in an oven at 180 °C until the inner tem­per­a­ture of meat reached 180 °C, which took an aver­age of 60 min­utes.

Sunflower and seed oils oxi­dized and failed to main­tain antiox­i­dant capac­ity com­pared to olive oil, which did not oxi­dize dur­ing roast­ing, the authors sug­gest­ing due to a higher toco­pherol con­tent. Clearly, the unprocessed oil sam­ples includ­ing olive oil, con­tained higher lev­els of phe­no­lic com­pounds, which after roast­ing was sig­nif­i­cantly reduced in all sam­ples. For exam­ple, ​“a dra­matic loss of 3,4‑DHPEA-EDA (98 per­cent) and 3,4‑DHPEA-EA (70 per­cent)” was found in OO sam­ples. However, the rad­i­cal activ­ity was higher for OO sam­ples, com­pared to other veg­etable oils.

Overall, OO degra­da­tion due to pro­cess­ing is a com­plex issue deter­mined by many dif­fer­ent fac­tors. Regardless of some ben­e­fits being shown toward deep fry­ing, high tem­per­a­tures of deep fry­ing do induce chem­i­cal changes such as oxi­da­tion, poly­mer­iza­tion, cycliza­tion, and hydrol­y­sis. However, com­pared to other veg­etable oils, OO is a bet­ter choice for cook­ing, regard­less of the method, as it is more resis­tant to the effects of oxi­da­tion and free rad­i­cal pro­duc­tion.

According to the authors of the study pub­lished in Food Chemistry 2015, ​“These chem­i­cal reac­tions are influ­enced by the type and qual­ity of the oil, the food prop­er­ties, and the food/oil ratio, among other para­me­ters.”

In con­clu­sion, OO and in par­tic­u­lar EVOO is con­sid­ered a healthy cook­ing oil over­all, espe­cially in com­par­i­son to other veg­etable oils. Minimizing cook­ing time and not reusing oils helps reduce oxi­da­tion and loss of phe­no­lic com­pounds. However, to main­tain the full ben­e­fits and bioac­tive com­pounds in OO the best way to con­sume it is raw, in its orig­i­nal unprocessed state.

• Food Chemistry 2015


• Food Chemistry Toxicology


• Journal of Agriculture and Food Chemistry


• Food Chemistry 2010


• Food Science and Technology


• Food Research International