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Polyunsaturated Fats

Also indexed as: Corn Oil, Flaxseed Oil, Hemp Oil, Pumpkin Seed Oil, Safflower Oil, Sesame Oil, Soybean Oil, Sunflower Oil

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Preparation, uses, and tips

Polyunsaturated fats are extremely vulnerable to damage from heat, so they are not suitable for high-temperature cooking. These oils are best used in salad dressings, sauces, and dips. To add flavor to grains and stir-fry dishes, sprinkle the cooked food with flaxseed oil just before serving.

Buying and storing tips

Polyunsaturated oils can become rancid when exposed to heat, light, and oxygen. As a result, oil-processing methods affect the nutritional content, storage life, and quality of oils. Choosing a high quality cooking oil can be a challenge unless one understands the terms that food manufacturers use to describe the methods by which cooking oils are processed. When purchasing cooking oil, it is important to review the label, and note the method of extraction, and whether the oil is refined or unrefined. Whenever possible, choose expeller-pressed, unrefined oils (see definitions below). Select oils in light-resistant plastic containers, or dark brown or green glass containers.

Extraction Methods

Mechanical (expeller) extraction

During mechanical extraction, an expeller press crushes the seeds, nuts, or vegetables to extract the oil. This pressing is done under intense pressure, and raises the temperature of the oil to 185 to 200°F (85–93.3°C). Typically, nuts and seeds are heated up to 250°F (120°C) before being placed in the expeller; heating makes the pressing more efficient. Some manufacturers produce “cold-pressed” oils—a term typically used to describe oil that was extracted without using additional external heat. This term is also used when cold water is run through the expeller, keeping the temperature of the oil from rising. However, there is no legal or binding definition of “cold-pressed,” so oils may be so labeled even when temperatures were quite high during pressing.

Solvent extraction

Solvent extraction is a more efficient and complete method of oil extraction, and is therefore the preferred method of large cooking oil manufacturers. During solvent extraction, nuts and seeds are cracked to expose the oil, and then combined with a chemical solution containing a solvent (typically hexane). The solvent pulls the oil from the nut or seed. The oil-solvent mixture is then heated to about 300°F (150°C) to evaporate out the solvent.

Refining Methods

Unrefined oils

Once the oil is extracted (either through mechanical or solvent extraction), manufacturers may simply filter the oil to remove some impurities and sell it as unrefined. Unrefined oil retains its full natural flavor, aroma, and color, and many naturally occurring nutrients.

Refined oils

To extend the shelf life of the extracted oil, some manufacturers refine oils. Refining can include as many as 40 different steps, including bleaching, deodorizing, and degumming. Refined oils are clear, odorless, and less flavorful than unrefined oils, and are more suitable for high temperature cooking. All polyunsaturated oils should be stored in the refrigerator or the freezer.

Varieties

Alpha-linolenic acid (ALA)

ALA is a member of the omega-3 family of fatty acids. It is called an essential fatty acid because the body cannot manufacture it—essential fatty acids must be consumed in the diet. Dietary sources of ALA include flaxseed, soybean, and pumpkin seed oil.

Eicosapentaenoic acid (EPA)

EPA is a member of the omega-3 family of fatty acids. The oils derived from cold-water fish (salmon, tuna, sardines, and cod) are concentrated sources of EPA. To a limited extent, the human body can make EPA from ALA.

Docosahexaenoic acid (DHA)

DHA is a member of the omega-3 family of fatty acids. This fatty acid is found in cold-water fish and in some types of algae.

Linoleic acid

Linoleic acid is a member of the omega-6 family of fatty acids. It is another essential fatty acid. Dietary sources of linoleic acid include sunflower seed, safflower, and corn oil.

Gamma-linolenic acid (GLA)

GLA is a member of the omega-6 family of fatty acids. Borage oil and evening primrose oil are rich sources of GLA.

Nutrition Highlights

Corn oil, 1 Tbsp (14g)
Calories: 120
Protein: 0.0g
Carbohydrate: 0.0g
Total Fat: 13.6g
Fiber: 0.0g

Flax oil, 1 Tbsp (14g)
Calories: 135
Protein: 0.0g
Carbohydrate: 0.0g
Total Fat: 15g
Fiber: 0.0g

Hemp oil, 1 Tbsp (14g)
Calories: 135
Protein: 0.0g
Carbohydrate: 0.0g
Total Fat: 15g
Fiber: 0.0g

Safflower oil, 1 Tbsp (14g)
Calories: 120
Protein: 0.0g
Carbohydrate: 0.0g
Total Fat: 13.6g
Fiber: 0.0g
*Good source of: Vitamin E 5.8 IU

Sunflower oil, 1 Tbsp (14g)
Calories: 120
Protein: 0.0g
Carbohydrate: 0.0g
Total Fat: 13.6g
Fiber: 0.0g

*Foods that are an “excellent source” of a particular nutrient provide 20% or more of the Recommended Daily Value. Foods that are a “good source” of a particular nutrient provide between 10 and 20% of the Recommended Daily Value.

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