The type of frying oil used depends on the application. Fried chicken requires oils with different characteristics than would be used with chips.
The food industry has spent millions of dollars in the past 10 to 15 years working to produce reduced- or low-fat foods and ingredients for such foods. Despite the industry's efforts, sales of rich, fatty foods continue to rise. (See Fried Snacks Sales chart.)

There is a good reason for this: fatty foods taste great! Fats carry flavor, pass on richness to foods and help provide the impression that a food is moist. Fatty foods also impart a feeling of satiety, which makes an individual feel good on several levels.

Overall, fats and oils perform a wide variety of functions. These include:

  • Emulsion formation
  • Lubrication
  • Shortening texture
  • Transferring heat
  • Imparting flavor
  • Carrying flavor
  • Functioning as antioxidants to protect flavor and nutrients and
  • Eliminating sharp melting points by softening over a wide temperature range.
It goes without saying that fats and oils contain more calories than proteins and carbohydrates on a weight for weight basis. And, many articles have addressed their role in health—both positive and negative. (See “Urging on Omegas” in this May 2003 issue.)

But fats and oils are an innate part of our food supply. Here is a closer look at how fats and oils function in foods, especially in baked and fried foods.

A double bond can be in a trans or cis configuration (shown here), depending on which side the hydroxyl groups are located.

Baked Goods Benefits

Fats and oils play a crucial role in the formulation and production of a wide variety of bakery items. One ingredient does not fit all, so suppliers also manufacture a wide range of shortenings, margarines and specialty fats and oils.

A quick review of oil chemistry provides a foundation to understand how these materials function. Fats or oils generally contain 96% to 98% triglycerides (or—from a chemist's view, more accurately called triacylglycerides). The molecules are structured to have three fatty acids attached to a glycerol backbone. Diglycerides have two fatty acids and monoglycerides have one. (See the illustration.) The fluidity or hardness of a blend of triglycerides depends upon the source of fat and how the product has been processed. Animal fats, coconut oil and hydrogenated products are harder and, thanks to higher concentrations of fatty acids, have higher melting points.

Most vegetable oils are fluid at room temperature, but the use of hydrogenation allows them to be modified to produce products with varying degrees of hardness. Hydrogenation is a process in which oils are exposed to hydrogen under pressure in the presence of a metal catalyst (usually nickel). Liquid oils are hardened or plasticized during hydrogenation through the formation of trans-isomers of the unsaturated fats. (See the Melting Point Comparisons chart.) These trans-fats act like saturated fats in that they have higher melting points than their cis forms.

The ability of a fat to soften and melt is an important characteristic during baking. Baking fats must have the ability to resist the hydrolytic effects of water as the moisture is “baked out” of the product. At the same time, the fat must cling to the cell wall surfaces of the dough. This “wetting action” is a result of the presence of mono- and diglycerides that act as surfactant compounds or emulsifiers. A surfactant is a compound that is soluble in both aqueous (water) and non-aqueous (i.e., oil) media.

Fats also remove energy from the dough as they cool—through their latent heat of crystallization. This allows products to “set up,” hence the use of high melting point fats in flaky pastries. Generally, the higher the percentage of saturated and/or trans-fats in the fat, the higher its melting point.

Baking fats also act as shorteners, hence the name shortenings. Shortenings reduce binding between protein and carbohydrate molecules, an action that softens and tenderizes baked goods' texture. This reduces or “shortens” the time it takes to chew or swallow a baked food. Shortenings also trap air during the whipping process, helping to establish the grain or cell structure in the finished product.

The physical characteristics of fats are highly dependent upon the type and position of fatty acids attached to the glycerol backbone.

Mimicking Moisture

The water in baked foods, especially cakes, muffins and breads, is bound to the carbohydrates and proteins. The moisture level is both low and “tied up,” so it is not “sensed” by the person eating the food. Yet, due to the fat, such products are perceived to be moist.

As fats in foods melt in the consumer's mouth, they coat and cool the tongue's surface. Low- or no-fat foods often appear dry because of the lack of fats. Mimicking this cooling and coating effect is one of the greatest challenges faced by R&D departments formulating reduced-fat products.

Suppliers are offering increasingly sophisticated fats and oils developed to meet the unique needs of various applications such as puff pastries, cakes, cookies, icings, breads, pie crusts, turnovers, tarts and croissants. For example, a puff pastry requires a high melting point with a high solid fat content to produce the desired flaky layers, whereas an all-purpose shortening melts at a lower temperature and is applicable for use in breads, cakes, rolls, or cookies. The chart “Solid Meltdown” shows the relationship between solid fat index and melting point, and how the many different specialty products perform.

The physical characteristics of fats are highly dependent upon the type and position of fatty acids attached to the glycerol backbone.

Transferring Heat

At some point in the far distant past, someone discovered that dropping foods into hot oil yielded a delicious product. Egyptian wall paintings show dough being cooked in hot oil, an excellent heat transfer medium. It cooks or fries food quickly and evenly and, depending upon the product, yields foods with a variety of desirable textures and flavors. Foods that might take 25 minutes to cook in an oven may be finished fried in 4-6 minutes.

Any fat or oil may be used for frying, but not every fat or oil will produce the desired finished product. Also, a fat or oil used at home for frying cannot necessarily be used for commercial frying. For example, virgin olive oil tastes good and is a popular cooking oil among television chefs, but it cannot be used in either industrial or foodservice frying because it breaks down quickly.

High-stability frying oils are required for industrial fryers and foodservice operations. Fifteen years ago, animal fats and blended fats (consisting of animal fats and vegetable oils) were in common use, especially in the foodservice industry. The relationship between saturated fats and heart disease resulted in their use being greatly reduced. They were replaced, in most cases, with products that had been stabilized through hydrogenation. The hydrogenation process reduces the degree of unsaturation (double bonds). The more double bonds, the greater the likelihood the oil will deteriorate.

Concerns about both saturated and trans-fats have prompted operators to look for other frying options. New oils with reduced levels of polyunsaturates from sources such as sunflower have been shown to have excellent frying properties, despite relatively high levels of monounsaturated fatty acids. The European response has been a product that is a blend of specially refined sesame and rice bran oils. Addition of this patented blend to bulk oil extends fry-life, and even protects the finished product. The product's natural antioxidants act as oxidation reaction chain breakers. One advantage to both these ingredients is that they are natural products.

The soy industry also is responding to the challenge. Through the “Better Bean Initiative,” scientists from the United States Department of Agriculture have been working to develop a low-saturated fat and low linolenic bean.

Although all these fatty acids are 18 carbons in length, their melting points vary greatly, depending on how many double (unsaturated) bonds they have and whether the double bond is in a cis or trans configuration.

Ends Determine the Means

The type of frying oil used depends on the application. When frying snacks, such as chips or nuts, many processors use liquid oils that have been “brushed” (lightly hydrogenated). Doughnuts are fried in harder fats to produce what amounts to a hard “shell” on the surface. This shell helps hold coatings, and the harder fats impart a less “greasy” mouthfeel. Frying doughnuts in a liquid product causes coatings or glazes to crack or bleed. Par-fried potatoes generally are produced in a hardened vegetable oil with a high melting point. The potatoes are cut, washed, par-fried and then flash frozen. They often are packaged in an inexpensive paper bag, especially when their destination is the foodservice industry.

The type of product being fried also affects oil performance. Commercial potato chip operations are much less abusive to oils than coated products. Batters and breadings contain ingredients such as salt and leavening agents that quicken oil degradation. Ironically, very fresh oil is not a good frying oil. A fat or oil must begin to break down to produce optimum quality fried foods. Old time bakers knew this and would add a cup of used oil to fresh oil. The old oil contained surfactants that improved the oil's contact with food. This is the basis of the surfactant theory of frying developed by Michael Blumenthal, Ph.D., in the late 1980s.

Partially pre-frying foods helps with later heating in microwave ovens. Research shows that heated and partially abused oils tend to focus microwaves, which cause surfaces to heat more rapidly.

However, manufacturers should maintain the quality of the oils used during frying. Cooking food in abused oil negatively impacts quality, flavor, shelf life and even food safety.

There has been much news about the “fattening of America.” However, the reality is that fats in food serve many desirable purposes, from flavor enhancement to imparting the sensation of moistness in cakes to assuring proper volume in doughnuts. Duplicating what fats do in baked and fried foods is a difficult task—the difficulty of which can be measured in the many low- and no-fat products that have failed in the marketplace.

Doughnuts have a less greasy mouthfeel when they are fried in hard fats with high melting points.

Website Resources—Article on frying fats—Formulation assistance in dealing with trans-fats—Series of articles on analytical
methods for lipids—American Oil Chemists' Society page, with links to related sites—More information on trans-fat alternatives—Article on cocoa butter replacer and omega fatty acids