Interesterified fat

Interesterified fats are oils that have been chemically modified (e.g., turning soybean oil into interesterified soybean oil). This is done in order to make them more solid, less liable to go rancid and more stable for applications such as deep frying. The interesterification process is used as an alternative to partial hydrogenation, which results in trans fats. However, research indicates that interesterified fats may pose health risks, some greater in magnitude than trans fats.

Chemistry
In a polyunsaturated fat, one or more polyunsaturated fatty acids (PUFA) are esterified to a glycerol backbone. Interesterification is used to replace the PUFA with a saturated fatty acid, typically stearic acid. The process can be applied to natural oils or fats, or hydrogenated or fractionated oils. It can be induced by chemicals or enzymatic catalysts. The interesterified fats can be separated through controlled crystalization. Interesterification does not introduce trans fatty acids. However, the resulting fat can be subtly different than natural oils.



In polyunsaturated fats, the PUFA is commonly found at the middle position (sn2) on the glycerol. Stearic acid is not usually found at sn2 in vegetable oils used in the human diet.

Health effects
Research has raised concern about some types of interesterified fats, suggesting that replacing a polyunsaturated fatty-acid molecule in vegetable oil with stearic acid might pose problems if the stearic acid is placed in the middle fatty-acid position of the triglyceride, since it is not as easily metabolized. Other, early research shows that highly-saturated interesterified fats may raise blood sugar levels even more than trans fats.