Partially Hydrogenated Vegetable Oil: What is It?

Read the extensive list of ingredients found on many prepared foods, and you will find the term "contains partially hydrogenated" cottonseed, soy, or some other vegetable oil. Although this describes the ingredient to a chemist, it doesn't say much to the average consumer. What does it mean to hydrogenate an oil, and why is the process of hydrogenation employed in so many products?

What Distinguishes a Vegetable Oil?

Vegetable oils are purified fats and are generally considered more healthful in the diet than animal fats. They are used to fry foods and perform other functions animal fats formerly performed, even though it is acknowledged that an animal fat such as lard can sometimes perform the task in superior fashion. (Who has not heard of legendary crust of Grandma's apple pie?)

Vegetable oils are moderately long-chained mixtures of organic compounds containing two or more double-bonded carbon atoms. Chemically, a double bond is drawn -CH=CH-. Such a bond is "unsaturated," since one can change the bond by adding an additional hydrogen atom to each unsaturated carbon. The former double bond is now a single bond, written -CH₂-CH₂-. If vegetable oil is not completely saturated, it is "partially hydrogenated."

Interestingly, Penn State Hershey Heart and Vascular Institute says "Foods made with partially hydrogenated oils should be avoided because they contain high levels of trans fatty acids, which are linked to heart disease." Thus, the hydrogenation process may remove much of the healthful benefit obtained through the elimination of animal fat. One might even ask if all the benefit is lost, or if the final situation could actually be worse?

The Hydrogenation Process

How is oil saturated? In order to accomplish the addition of hydrogen to double bonds, a chemical reaction is carried out. Hydrogen is added with the aid of a catalyst-generally one or more finely-divided platinum metals. The oil is heated with the catalyst, and the hydrogen is bubbled through the heated oil, absorbing it.

Why is this process utilized? The process is not used with the goal of negatively affecting your food. Oils that are treated in this way can be made solid or semi-solid, resulting in better performance in baking and in other qualities. To formulate without this process would require more expensive ingredients, in a competitive market making products less saleable.

References and Resources:

Ohio State University, "Chemistry and Processing of Hydrogenation," by David B. Min.

Health and Goodness - "What is Hydrogenated Vegetable Oil?" by Jane Thurnell-Read.

Harvard School of Public Health - "Shining the Light on Trans Fat"