By Donna Berry, Contributing Editor
The fatty-acid composition of fats and oils controls their functionality and nutritional profile. Balancing the two can be difficult, because they are often diametrically opposed, with less-healthful fats often providing the most-desirable functionality. This challenges product designers in applications where fat directly influences product performance and shelf life.
The one attribute all fats and oils have in common is that they are concentrated sources of energy that deliver 9 calories per gram, explains Bob Wainwright, technical director, oils & shortenings, Cargill, Minneapolis. “Beyond that, it is difficult to generalize," he says. “For example, land-based animal fats and some vegetable fats, such as palm, are semisolid at room temperature. Other vegetable sources are liquid at room temperature, as are animal-based fish oils. Algal oils tend to be liquid and highly unsaturated; however, more-saturated derivatives are in development. Animal fats from ruminants contain naturally occurring trans fatty acids, while vegetable and non-ruminant derivatives do not. Animal fats and oils contain cholesterol, while plant-based derivatives do not. So, the source is especially relevant to performance, functionality and nutritional impact."
A quick review
Before one attempts to balance functionality and nutrition, it is essential to understand the chemical structure of fats and oils, which are almost always triacylglycerols (a glycerol backbone esterified to three fatty-acid chains consisting of carbon molecules connected to hydrogen molecules). Those three fatty acids are seldom the same, regardless of source. One fatty acid may be saturated (no double bonds), while the other two might be unsaturated. (One double bond is referred to as monounsaturated, or MUFA, while two or more double bonds is referred to as polyunsaturated, or PUFA.) If the triacylglycerol has undergone partial hydrogenation, one or both of the unsaturated fatty acids may be in the trans configuration, rather than in the traditional cis configuration. The trans orientation makes the fatty acid less flexible, with more solid-like properties.
Saturated fatty acids are typically solid at room temperature and are inherently the most-stable type of fatty acid. Stability refers to susceptibility to oxidation, which takes place when a double bond breaks and an oxygen molecule attaches. Saturated fatty acids have no double bonds, hence they are considered highly stable. Therefore, the least-stable fatty acids are those that have a long carbon chain with multiple double bonds.
The majority of unsaturated fatty acids in the human diet contain 18 carbons. However, they can contain as few as 10 carbons and as many as 22, with the former mostly found in animal fat and the latter in marine oils. The “omega" nomenclature system, which identifies the carbon that begins the first double bond counting from the methyl end of the fatty acid, helps categorize fatty acids in terms of function and nutrition.
For example, of the 18-carbon-chain fatty acids, oleic acid has one double bond starting on the ninth carbon from the methyl end, and is appropriately referred to as an omega-9 fatty acid. Linoleic acid and linolenic acid (also often referred to as alpha-linolenic acid, or simply ALA) are also 18-carbon-chain fatty acids. Linoleic has two double bonds, the first occurring at carbon six (from the methyl end) and is referred to as an omega-6, while ALA has three double bonds. It is classified as an omega-3, as the first double bond occurs at the third carbon.
Two other popular omega-3 fatty acids are eicosapentaenoic acid (EPA), which has a 20-carbon chain and five double bonds, and docosahexaenoic acid (DHA), which has a 22-carbon chain and six double bonds. As you can imagine, these long-chain fatty acids with numerous double bonds are highly unstable for certain food applications, in particular those that involve high heat, as frying and baking temperatures accelerate oxidation.
The nutrition angle
But the body appreciates this instability. This is where that diametrical opposition (functionality vs. nutrition) comes into play. “In general, trans and saturated fatty acids have been shown to raise total and low-density lipoprotein (LDL) serum cholesterol levels, the bad cholesterol, while most monounsaturated and polyunsaturated fatty acids have been shown to lower total and LDL serum cholesterol levels," says Tom Tiffany, senior technical manager, ADM, Decatur, IL. “Overall, the goal is to consume a greater proportion of unsaturated fatty acids compared to saturated and trans fatty acids within the context of a healthy balanced diet."
Gerald McNeill, vice president of R&D, Loders Croklaan North America, Channahon, IL, says it is important to recognize that, while fats and oils are crudely categorized as “saturated" or “unsaturated," they are actually composed of combinations of saturated and unsaturated fatty acids. In other words, it is not always fair to characterize a fat as “good" or “bad."
“For example, the fatty-acid composition of palm oil, which is a highly functional, natural, solid fat, is about half unsaturated and half saturated," McNeill says. “Clearly, the ‘good’ unsaturated fatty acids cancel out the ‘bad’ saturated fatty acids and palm oil should be considered neutral."
To clarify, it’s the fatty acids that have the good and bad reputation, not the fat or oil ingredient. And when it comes to trans fatty acids, the National Academy of Sciences says: “Trans fatty acids are not essential and provide no known benefit to human health.… As with saturated fatty acids, there is a positive linear trend between trans-fatty-acid intake and LDL cholesterol concentration and, therefore, increased risk of coronary heart disease (CHD) … any incremental increase in trans-fatty-acid intake increases CHD risk."
Further, Christine Bunting, director, product application & technical support, Martek, a division of DSM Nutritional Products, Columbia, MD, points out that some research shows that trans fatty acids are also believed to reduce high-density lipoprotein (HDL) serum cholesterol, a.k.a., good cholesterol, making them the unhealthiest of all fatty acids.
Good vs. bad
But Tiffany reminds us, “Fats and oils used in the food industry are mixtures of fatty acids, so simply focusing on one class of fatty acids doesn’t reflect how a fat or oil will impact serum cholesterol levels."
