Unrefined, cold pressed virgin olive oil (VOO) is rich in interesting compounds including many unique antioxidants. Without them, olive oil would not be the healthy oil it is. A number of studies have looked at how cooking affects those antioxidants and VOO generally. This research definitely contradicts current wisdom that we should not use our good olive oils for cooking at other than very gentle heat.
In one study, a variety of vegetables (zucchini, potatoes, eggplant, and green peppers) were fried in VOO for 5-8 minutes until browned; zucchini and eggplant were batter fried as well. The amount of olive oil antioxidants, such as tyrosol and vitamin E, increased in the vegetables during cooking. While the quality of the left over oil deteriorated, the vegetables improved. The batter-fried vegetables did not gain much but the breading gained antioxidants. Overall, frying in VOO improved the quality of the vegetables.
Homemade tomato sauces traditionally add VOO to fresh or canned tomatoes and cook them for anything from a few minutes to many hours. When tomato sauce is cooked by itself, its antioxidant content drops. In contrast, when VOO is added, antioxidants increase, even in sauces simmered for 6-10 hours. This benefit seems to be specific to VOO: When tomato sauces made with sunflower oil were compared with those made with VOO only the VOO increased the antioxidant activity in the volunteer’s blood. This is key because ultimately our goal is to increase our own antioxidant status, not that of our foods. So this effect on the human body is important.
One of the problems with processed starchy foods, and especially potato chips and French fries, is that acrylamides form as these foods crisp and brown. Acrylamides are linked to both cancer and dementia. One study heated 20 different types of VOO in a deep fat fryer. Almost no antioxidants were lost during the first 15 minutes of heating, and 30 to 50% of the most unique antioxidants remained undamaged 4 hours later. This means that VOO’s antioxidants are very heat stable. Next sliced potatoes were deep fat fried for 5, 10, or 15 minutes in the various olive oils. All of the potato chips formed acrylamides but the chips fried in the most antioxidant-rich VOOs formed vastly fewer. Ultimately, VOO worked as well as a high heat tolerant mix of sunflower seed, cottonseed, and palm oil for panfrying but actually was healthier for deep fat frying, thanks to its antioxidants. None of the refined oils currently recommended for high heat cooking contain these unique, heat resistant VOO antioxidants.
All animal foods form troubling carcinogenic heterocyclic amines as they brown. Many scientists think that meats dramatically increase cancer rates because of these heterocyclic amines, known to damage DNA. In Mediterranean cooking, meats are typically marinated in VOO, herbs, and wine before they are cooked. In addition, as the meat, chicken, or fish cook, they are basted with VOO in lemon or wine mixtures. This exposure to powerful antioxidants dramatically reduces the formation of carcinogenic compounds. As VOO ages, it loses antioxidants – – up to 40% can be lost over a year’s time. Cooking with older olive oils increased the amounts of heterocyclic amines but never to the degree of meats cooked without VOO.
Fish also form these toxins in response to heat. Canned fish (tuna, sardines, etc.) are exposed to heat in the canning process. When fish canned in soybean oil, water, refined olive oil and VOO were compared, the toxin formation was much lower in fish bathing in VOO. The antioxidants apparently formed a surface barrier that protected the fish from heat damage. Similarly, fresh fish (sardines, anchovies, hake, etc.) fried in VOO also absorbed important antioxidants from the oil during frying and generated far fewer troublesome amines.
These studies strongly indicate that, not only is it fine to cook with a good quality cold pressed olive oil, VOO actually is our best cooking oil from a health perspective. These studies tested olive oil at temperatures of 350 degrees F. That is the temperature a skillet on high heat generally reaches and a common temperature in home cooking. For instance, electric deep fat fryers sold for home use are set to cook at 350 F. In contrast, commercial fryers are often operated at higher temperatures, temperatures where some benefits of VOO may be lost. Studies, however, also suggest that, while the refined oil recommended for very high heat cooking may not break down at higher temperatures, they also lack antioxidants and fail to protect against the formation of toxic compounds and the destruction of beneficial compounds as our food cooks. Conclusion: A good quality, cold pressed extra virgin olive oil should be our choice not only for salad dressings and dipping for French bread but also for cooking, including some deep fat frying.
Photograph: Mediterranean Food Tomatoes Red Eat Cook by Anelka
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