The Laboratory Notebook

Answering important questions about quality.

By Robert Green

This issue we explore the important and timely topic of analyzing fatty acids with emphasis on the upcoming change to the Nutrition Facts panel requirements adding trans fat disclosure.

Q. I produce a nutrition bar and have heard that I must soon determine and report the amountof trans fat in it. Please explain this issue and tell me how to comply.

A. Let’s start at the top. Lipids are a large and diverse group of naturally occurring organic compounds that are characterized by their solubility in certain organic solvents (such as ether, chloroform and acetone) and general insolubility in water.

Included in the lipid family are mono, di and triglycerides, sterols, terpenes, and fatty acids. Although there are some differences, fatty acids are often referred to as “fats.” Fats are an important source of dietary energy and a major form of energy storage. Fatty acids are also intermediates in the synthesis of other important compounds, such as phospholipids. They are also critical in the absorption of the fat-soluble vitamins A, D, E and K.

Fatty acids consist of chains of carbon atoms with attached hydrogen atoms. A fatty acid that has all carbon atoms attached to each other with single bonds and the maximum number of hydrogen atoms attached to every carbon atom is said to be saturated with hydrogen atoms and is referred to as a saturated fatty acid. Examples of saturated fatty acids are stearic, myristic and lauric acids.

There are also fatty acids that do not have the maximum number of hydrogen atoms. Instead, two carbon atoms are connected by a double bond without a hydrogen atom in between. Since it is not saturated with hydrogen it is referred to as “unsaturated.” If the fatty acid has only one location where the carbon atoms are connected it is referred to as “monounsaturated” and when there is more than one such connection it is referred to as “polyunsaturated.” Examples of unsaturated fatty acids are linoleic, palmitoleic and oleic acids.

Foods are generally a combination of saturated, monounsaturated and poly­unsaturated fatty acids. Foods of animal origin lean towards the saturated fatty acids, while plant origin foods lean towards the unsaturated types.

Saturated fatty acids tend to be stable; they do not easily combine with oxygen and turn rancid. Unsaturated fatty acids, on the other hand, are much less stable and have a tendency to combine with oxygen and turn rancid.

In today’s market we want the best of both worlds—stable unsaturated fatty acids. Food processors discovered that this can be accomplished by adding hydrogen to unsaturated fatty acids. The process is called “hydrogenation.” This process converts liquid oils, like vegetable oils, to solids, such as shortenings and hard margarines. Hydrogenation rearranges hydrogen atoms around the carbon double bonds. Initially unsaturated fatty acids have all of the atoms on the same side of the carbon chain. This is referred to as “cis” fatty acids, so named because in Latin the word “cis” means “same.” A result of hydrogenation is the rearrangement of the hydrogen atoms with them ending up on opposite sides of the chain. This configuration is called “trans” fatty acids, as the word “trans” means “across” in Latin.

We now all know that saturated fats and trans fats raise the “bad cholesterol” or LDL. While the Nutrition Facts panel has been required to list total fat and saturated fat for some time, there currently is no similar requirement for trans fat. That’s all about to change.

Effective January 1, 2006, the a­mount of trans fat must be listed in the Nutrition Facts panel on a separate line under saturated fat. As with all governmental rules there is an exception; trans fat does not have to be listed if the total fat in a food is less than 0.5 grams per serving and no claims are made about fat, fatty acids or cholesterol content. If trans fat is not listed, a footnote must be added stating that the food is “not a significant source of trans fat.” Note the 0.5 gram exception relates to total fat in the product and not just trans fat as has been incorrectly reported elsewhere.

So how do we determine the amount of trans fat in your product? Until relatively recently we could not. That’s because the analytical techniques used to determine fats in foods were not capable of separating cis and trans fats. Fortunately, that has all changed.

Gas Chromatography (GC) has been the analytical method of choice for the determination of total fat, saturated fat, and mono- and polyunsaturated fat in foods. You may recall from an earlier column that GC involves a sample being vaporized with the resulting gas analyzed chromatographically. A gas chromatograph consists of an injection port, a flowing mobile phase, a separation column containing the stationary phase and a detector. The organic compounds are separated due to differences in their partitioning behavior between the mobile gas phase (usually helium, argon or nitrogen) and the stationary phase in the column.

To analyze fatty acids they must first be extracted from the food product. This is generally accomplished by acidic hydrolysis for most foods, alkaline hydrolysis for dairy products and a combination of both for cheeses. The fat is then extracted into ether and then derivatized through methylation (that is, the addition of methyl alcohol) resulting in fatty acid methyl esters, which are non-reactive derivatives of fatty acids and are also more volatile than the free acid components. The sample is then injected into the GC and transported through the separation column. Once separated, the analyte of interest is identified and measured by the appropriate detector.

Techniques generally in use for fatty acid analysis are unable to separate the closely related cis and trans isomers. Thanks to the introduction of longer columns, we can now effect the separation, and once separated, we can identify and quantify cis and trans fatty acids by a flame ionization detector. And when I say long columns I mean it…these babies are 100 meters (that’s 300 feet!).

Because of the required length of travel, a typical analytical run takes over an hour to complete. And since time is money, expect to pay a bit more for these analyses.

So now if your product contains trans fat you know what you need to do and how to do it.NW