Potential Health Effects of Pan Fried Vegetables in Virgin Olive Oil Following the Mediterranean Traditional Culinary Practice

Frying is a very old cooking technique, used as early as 1600 BC by the ancient Egyptians and later by the Greeks and the Romans¹. Frying improves the sensory quality of food by forming aroma compounds, and providing attractive color, crust and texture. As a result of their unique and delicious sensory characteristics, fried foods are consumed worldwide with sustainable popularity, despite their considerable fat content and the consumers’ awareness of the relationships between food, nutrition and health².

Olive oil and vegetables hold a key position in Mediterranean diet, the central elements of which are variety, reduction of saturated lipids and animal proteins, emphasis on olive oil and an abundance of vegetables, fruits, grains and legumes³. Pan-frying of vegetables, such as potatoes, green peppers, zucchini, eggplants- in olive oil is a common practice in the Mediterranean olive oil producing countries. Vegetables are normally fried as they are, although sometimes eggplants and zucchinis are blanketed with flour or batter prior to frying. The fried vegetables are either served as starters, or used as ingredients in other Mediterranean recipes (eg mousaka).

Research has indicated that, contrary to common belief, frying appears to have the same or even less effect on nutrient and vitamin losses compared to other cooking methods^4,5, while the nutritive value of food may increase due to the absorption of frying oils, which are usually rich in unsaturated fatty acids and vitamin E.

Virgin olive oil (VOO) holds a unique position among cooking oils and fats, being very rich in monounsaturated fatty acids and containing significant amounts of health-promoting microconsituents like tocopherols, polyphenols, terpenic acids, squalene and phytosterols.

Monounsaturated fatty acids are considered as potentially beneficial for cardiovascular heart disease risk reduction.

Tocopherols are considered as the most important lipid phase natural antioxidants, which prevent lipid peroxidation in membranes and lipoprotein particles.

Polyphenols are known to possess antioxidant capacity with respect to oxidative alterations and have been associated with lower risk of coronary heart disease, some types of cancer and inflammation.

Olive oil’s terpenic acids -oleanolic, maslinic and ursolic- have been reported to exhibit hepato-protective, anti-inflammatory and antitumor action.

Squalene, together with phenolic compounds and oleic acid appear to confer the anti-inflammatory properties and may contribute to the reported anti-carcinogenic activity of olive oil, especially for colon cancer.

Plant sterols are considered as important dietary components for lowering LDL cholesterol and maintaining good heart health, and they possess anticancer, anti-inflammatory and antioxidant activities.

During controlled pan-frying experiments of vegetables in VOO under household conditions, it was shown that a significant fraction of these substances survive and enrich the fried vegetables, thus becoming part of our diet^6,7. More specifically it was documented that, despite differences in size, shape, texture and culinary practice, the pan-fried vegetables:

1. were enriched in monounsaturated fatty acids, having a healthy fatty acid profile and low atherogenic and thrombogenic indices⁶
2. contained 70-350 times more ·-tocopherol than the fresh vegetables⁷
3. contained 4-13 times more VOO originating polyphenols–mainly tyrosol- compared to the raw vegetables⁶
4. were enriched in olive oil’s terpenic acids (oleanolic, maslinic, and ursolic acids)- which were not present in raw vegetablesin concentrations ranging from 2.1-6.8 mg/100 g of fried food⁷
5. contained 2-3 orders of magnitude more squalene compared to the raw vegetables⁶
6. were enriched in phytosterols in relation to the uncooked vegetables⁶.

Furthermore, it was calculated6,7 that a serving of vegetables panfried in VOO provides a significant portion of the daily intakes of these microconsituents, contributing to the intake of oleic acid, vitamin E, polyphenols, terpenic acids, squalene and plant sterols in the Mediterranean diet.
In conclusion, pan-fried vegetables as part of a balanced diet have a place in the diet, when done with virgin olive oil used for no more than two or three times for frying.