Friday, December 18, 2009

Are trans fats created when you heat olive oil or sunflower oil beyond their smoking points?

I think this answers your question more accurately:





Q. How exactly is trans fat created? If I bake with some (say, 1/4 cup) oil in a batter, does that make trans fats?





A. We’ve all read a lot about the dangers of trans fats. Most of the trans fat in our diet comes from artificially hydrogenated oils that are still widely used in food manufacturing. But did you know trans fatty acids also occur naturally? The natural trans fatty acids found in milk and other foods are not considered to be a health threat. In fact, one naturally-occurring trans fatty acid called conjugated linolenic acid, or CLA, is thought to have many beneficial effects in the body.





The trans fats you need to watch out for are the ones created by artificial hydrogenation. These “Franken-fats” are polyunsaturated fatty acids (PUFAs) that have been twisted into an unnatural configuration called a trans-isomer. This means that the molecule contains the exact same number and type of atoms as it did before, but they are arranged in a different shape.





But what a difference that small change makes! Polyunsaturated fats and their trans-isomers produce completely opposite effects in the body. While PUFAs help to improve cholesterol profiles and reduce your risk of heart disease, trans fats contribute to heart disease by fueling inflammation, raising bad cholesterol and lowering good cholesterol.





What does it take to create a “Franken-fat”?





Artificial hydrogenation involves mixing polyunsaturated oils with hydrogen atoms under very high pressure--not something you could accidentally do at home! High heat can also cause PUFAs to trans-isomerize into trans fats, if it is applied for long enough. For example, you have to heat a polyunsaturated oil to 240 dgrees F for 16 hours before it begins to trans-isomerize into trans fats--and even then, only a very small percentage (less than 1%) are converted.





As you can see, normal cooking temperatures and times are not nearly enough to create any significant amount of trans fats in the foods we cook at home.





Reference: Wolff, R. L. 1993. Heat-induced geometric isomerization of alpha-linolenic acid: effect of temperature and heating time on the appearance of individual isomers. Journal of the American Oil Chemists Society 70(4): 425-430.Are trans fats created when you heat olive oil or sunflower oil beyond their smoking points?
The smoke point generally refers to the temperature at which a cooking fat or oil begins to break down to glycerol and free fatty acids. So, at this point trans fats are formed.





In practice, any monounsaturate heated to smoking point turns into a trans fat. smoking point of olive and sunflower oil are 240 degree C and 107 degree C resply. When you heat to this temperature trans fats are formed.

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