June 1, 2003

17 Min Read
Fats' Chance

Edible fats and oils, alone or when in foods, face the threat of oxidation — an irreversible, adverse chemical reaction — from the moment they are exposed to the atmosphere. Antioxidants, by slowing oxidative degradation, give fats a chance to not bear the blame for foods’ demise.

“Guarding against oxidation is a constant battle and frequently requires protective ingredients (antioxidants) to be added directly into food products,” says Jeff Hunsicker, global vitamin E product manager, Cognis Nutrition & Health, LaGrange, IL.

Lipid oxidation occurs when atmospheric oxygen combines with unsaturated fatty acids (those with one or more double bonds), producing peroxides that further break down into aldehydes, ketones, acids and alcohols. These compounds can have a negative effect on food’s appearance, odor and taste. This is described as rancidity. Rancidity manifests itself in an array of ways, including making a food taste fishy, “painty” or cardboard-like. It can dull the color of food and change its nutritional composition. In meat products, it can result in a condition referred to as warmed-over flavor (WOF).

WOF is a rancidity phenomenon that occurs in cooked refrigerated and frozen meats. It can arise in either the four-minute, microwave-ready packaged beef tips in gravy or Sunday’s leftover pork roast. WOF develops during the very early stages of lipid oxidation and is very challenging to control.

Most fats contain a mixture of fatty acids, so fats are categorized according to their predominant fatty acids, i.e., saturated fats have high levels of saturated fatty acids. However, even saturated fats contain some unsaturated fatty acids, which are susceptible to oxidation.

In addition, prepared foods described as low in fat, or even fat-free, most likely contain small amounts of fatty acids, some of which are unsaturated. Thus, food formulators are rarely off the hook when it comes to preventing fat oxidation. A small amount of oxidized fat, and subsequent development of rancidity, can ruin a food.

For example, skim milk — which is virtually free of fat — contains trace amounts of phospholipids that are rich in polyunsaturated fatty acids. When these polyunsaturated fatty acids oxidize, the resulting off-flavors can make a consumer throw out a gallon of milk days before its expiration date.

“In addition to reducing the quality and nutritional value of foods, some end products of lipid oxidation — such as peroxides, aldehydes and ketones — have been shown to be harmful to human health,” says Stephen Byrd, technical service technologist, Eastman Chemical Co., Kingsport, TN.

Antioxidants, which block formation of free radicals by donating electrons or hydrogen ions to halt the oxidative process, can slow oxidation and, hence, rancidity development. Thus, antioxidants lengthen the shelf life of foods. In general, the more double bonds, or the higher the degree of unsaturation, the greater the probability that the fatty acid will be oxidized if left unprotected. However, Byrd says it is important to note that “rancidity can also be caused by enzymatic changes in fats and oils, which differs from oxidative rancidity and is not prevented by the use of antioxidants.”

Several factors catalyze oxidation; thus, controlling these variables also slows oxidation. For example, heat, light, trace metals (e.g., copper, nickel, iron and other pro-oxidant metals), various pigments, alkalinity and degree of unsaturation all can affect oxidation rate. Oxygen availability also affects oxidation, with more available oxygen increasing susceptibility to the reaction.

The addition of sequestering and/or chelating agents — such as citric acid; ethylenediaminetetraacetic acid (EDTA), which occurs as calcium disodium EDTA and disodium dihydrogen EDTA; and phosphates — can control trace metals. These ingredients inhibit metals from initiating undesirable lipid oxidative reactions by forming strong complexes with the metal ions.

The use of citric acid is well-established in meat products with high iron contents. USDA allows manufacturers to add citric acid to meat products at levels up to 100 ppm based on final product weight.

EDTA is effective in blocking copper and iron from catalyzing oxidative chain reactions. It is FDA-approved for use in various vegetable-oil-based products, such as margarine, mayonnaise and salad dressing, as well as a variety of canned vegetables and fish products. Average approved use levels range from 75 to 300 ppm.

Phosphates are primarily added to meat products to improve moisture retention. However, both sodium tripolyphosphate and tetrasodium pyrophosphate will sequester metal ions, greatly reducing rates of oxidation.

One way to reduce the chance of lipid oxidation in foods is to use saturated fats; however, the chances that a product developer would go out of his or her way to formulate with fats high in saturated fatty acids is highly unlikely in this day and age. After all, most consumers recognize the link between saturated-fat consumption and increased risk of coronary heart disease.

As a result, food formulators are turning away from saturated fats and oils and looking toward fats and oils containing high levels of monounsaturated and polyunsaturated fatty acids. This makes fatty-acid profiles on Nutrition Facts panels more appealing to consumers, but it also creates oxidation concerns for food manufacturers — and creates an opportunity for antioxidant use.

“Usually all oils require the addition of some type of antioxidant — synthetic or natural — to prevent rancidity and increase shelf-life,” says Lewis G. Jacobs, vice president technical services, Archer Daniels Midland Company (ADM), Natural Health & Nutrition Division, Decatur, IL. “The rancidity is due primarily to oxidation at the unsaturated, or double bond, sites. The more polyunsaturated the oil, the more prone it is to oxidation. Seed or vegetable oils usually contain various levels of natural antioxidants — tocopherols, tocotrienols, polyphenols, carotenoids, — while animal and marine oils are lacking these natural antioxidants and most certainly require the addition of either synthetic or natural antioxidants.”

The most-commonly used man-made antioxidants are butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate and tertiary-butylhydroquinone (TBHQ). Several considerations come into play when deciding if a product designer should choose these for a food.

“When selecting an antioxidant, like with all food ingredients, make sure it is approved for use in the country in which the product will be sold or the application in which it will be used,” Byrd says. “An example of an application-related consideration would be breakfast cereals. FDA regulations allow BHA and BHT to be used at a maximum level of up to 50 ppm, alone or in combination, based on product weight. TBHQ and propyl gallate are not approved for use in this manner, but can be added to cereals based on the fat weight of the product.”

It is important for food formulators to determine what type of fat or oil the food product will use. As Byrd notes: “If it will contain unsaturated vegetable oil, TBHQ would be the best choice, followed by propyl gallate. If animal fat is to be used, then BHA, BHT or tocopherols could be considered as well.”

BHA is a white waxy solid comprised of a mixture of two isomers, the 2-isomer and the 3-isomer. The 3-isomer is the more-effective antioxidant and generally makes up a minimum of 90% of commercial BHA products. The 3-isomer has very good solubility in fats and oils, and makes a very effective antioxidant in animal fats, but is rather ineffective with vegetable oils. It survives various heat processes, including frying and baking, enabling BHA to remain active and impart stability to finished products such as baked foods. Because BHA is volatile, it can be added to packaging materials. FDA has approved its use alone or in combination with other antioxidants, in dry potato products, dry beverage mixes, dry dessert mixes, breakfast cereals, dry fruits and shortenings.

BHT is a white crystalline solid with properties and approved applications similar to BHA. It is relatively ineffective in vegetable oils but is somewhat more effective than BHA. BHT shows good synergism with BHA, with the combination of BHT and BHA being a more-effective antioxidant than either used alone. BHT survives heat processing, thus carrying through into finished products. Being volatile, BHT can also be used in packaging materials.

Propyl gallate is a white crystalline solid that imparts good stability to vegetable oils and animal fats. It has good synergism with both BHA and BHT, but FDA regulations do not allow for its use with TBHQ. Because propyl gallate is heat-sensitive, decomposing above its melting point of 298ºF, it does not carry through into heat-processed foods. Propyl gallate also does not easily dissolve in fats and oils, and can form undesirable colored complexes with trace minerals. Adding citric acid can prevent this. Common applications include fats, oils, meat products and potato products.

TBHQ is a white to light-tan powder. It is considered as one of the most-effective antioxidants for most fats and oils, especially vegetable oils, with excellent oxidative stability achieved at much lower levels than those of other antioxidants. The effectiveness of TBHQ increases as the degree of unsaturation in the oil increases. Studies have shown that adding just 0.02% TBHQ to soybean oil increases stability almost four times that observed in soybean oil without added antioxidant. TBHQ has excellent carry-through in frying oils and good carry-through in baking applications. FDA has approved the use of TBHQ up to 200 ppm in most foods, based on the food’s fat content, except in applications where standards of identity prohibit its use.

With all-natural food products becoming increasingly more popular in today’s marketplace — most likely because of consumer demand for foods with ingredients they can pronounce — food manufacturers are steering away from synthetic antioxidants and looking to Mother Nature for help in controlling fat oxidation.

Many naturally occurring compounds possess antioxidant properties, and FDA recognizes some as official antioxidants. Others are categorized as flavor extracts, spices or even simply food, with their antioxidant properties touted as a benefit by suppliers.

Tocopherols are probably the best-known natural antioxidant and are recognized as such by FDA. “Tocopherols are nature’s antioxidants,” Hunsicker says. “They are found in vegetable oils, as well as grains, seeds and nuts. They protect fats and oils from oxidation, thus extending shelf life naturally.”

Because they are naturally present in vegetable oils, further addition of these antioxidants does not significantly improve oxidative stability of vegetable oils. Tocopherols work best in food products that are deficient in antioxidants, such as animal fats like butter and lard, as well as prepared foods that contain a mixture of fats.

Tocopherols exist in four forms — d-alpha, d-beta, d-gamma and d-delta — with the gamma and delta forms the most active for stabilizing fats and oils in food products. The alpha form is recognized for its nutritional value as vitamin E.

Products containing the four forms are referred to collectively as mixed tocopherols. Mixed tocopherols are added to foods for antioxidant functionality rather than for vitamin-E fortification, as the level of alpha-tocopherol is quite low. Mixed tocopherols allow food manufacturers to use an all-natural label statement.

“Most fat-containing foods derive protection from mixed tocopherols, especially animal and marine fats, but other oils derive additional benefits from the addition of antioxidants,” notes Jacobs. “The increase in shelf-life depends upon the type of oil and the amount of other natural antioxidants present. The protection is the result of termination of auto-oxidation, singlet oxygen quenching, free-radical scavenging and the neutralization of other oxidizing agents — nitrogen oxides, ozone, peroxides, etc. Foods that contain lower amounts of fatty substances are less likely to benefit significantly from added antioxidants, for peroxidation in such foods is not the major source of spoilage as with highly unsaturated fats.”

Natural mixed-tocopherol antioxidants isolated from vegetable oils “do not impart flavor, color or odor to final food applications and are effective at very low concentrations. Because they are resistant to high temperatures, they can be added early in processing to reduce water and simplify operations,” says Hunsicker.

The antioxidants are available in different forms for various applications, according to Hunsicker: “A spray-dried, water-soluble powder can be easily added to spice blends and other dry ingredients, whereas a fat-soluble form uses vegetable oil as a carrier and readily mixes in with fat ingredients.”

USDA allows tocopherols to be added to meat up to 300 ppm, a level that somewhat extends shelf life. To further extend it, other ingredients that work synergistically with tocopherols can be added. Ingredients such as ascorbyl palmitate, ascorbic acid and citric acid donate hydrogen atoms to oxidized tocopherols, recycling them for additional termination reactions.

“Mixed tocopherols do exhibit synergies with other natural antioxidants, such as polyphenols, vitamin C, carotenoids, lecithin, sterols, etc., as well as chelating agents, such as citric acid, phosphoric acid, etc.,” explains Jacobs. “This synergy plays an important role, in particular when the food system is complex and several different mechanisms are in play.”

FDA allows the use of tocopherols in most other food applications, with no level restriction when used in accordance with Good Manufacturing Practices. Typical usage levels are 0.01% to 0.02% of a food’s total fat content. Food products formulated with tocopherols typically state its inclusion in the ingredient statement as “Natural vitamin E added to preserve freshness,” or “Natural vitamin E added to protect flavor.”

According to Jacobs, another area that seems to be very active in adding natural antioxidants, especially mixed tocopherols, is the pet-food market. “Other animal-feed producers also are starting to turn from the traditional synthetic antioxidants in favor of natural,” he adds.

Certain spices contain phenolic compounds, which can delay the onset of oxidation. These compounds neutralize the oxidation reaction by contributing hydrogen ions from their hydroxyl groups to unstable free radicals formed during the initiation of oxidation. The phenolic compounds turn into free radicals; however, they are more stable than the initial free radicals involved in oxidation. Thus they don’t prevent oxidation. They slow its progression, naturally.

Due to their sensory profiles, such spices are usually used in meat, poultry and fish applications; however, they can be used in any fat system where the spice flavor complements the food’s overall flavor profile. Also, some suppliers have identified extraction methods that remove many of the characterizing flavors and aromas from spice extracts, rendering them virtually taste-free at levels used for antioxidative purposes.

Besides meat, poultry and fish, rosemary extract has application in mayonnaise, salad dressing, nuts and snack foods. Some confectionery and baked goods have even benefited from the addition of levels below the flavor threshold for rosemary. Such low levels still provide antioxidative benefits.

The active antioxidative compounds in rosemary include carnosol, carnosoic acid and its esters, and lesser amounts of rosmanol, rosmaridiphenol and rosmarinic acid.

While rosemary has been shown to be effective in prolonging the shelf life of traditional food products, it also helps prevent off-flavors and delay color loss in irradiated ground beef. Irradiation is an effective and safe method to decrease pathogens and spoilage bacteria; however, it actually promotes the formation of free radicals, causing an increased rate of color loss. “

By adding Fortium™ R10 rosemary extract to ground beef prior to irradiation, research has proven that color loss can be delayed significantly,” says Ann Rolow, technical sales manager, Kemin Americas Inc., Des Moines, IA.

Rosemary is likely the most widely used spice for its antioxidative properties; however, other spices, including sage, oregano and thyme, possess similar phenolic compounds. An oleoresin of sage has been shown to be effective in inhibiting flavor and color degradation due to oxidation. Direct applications include seasoning blends, salad dressing mixes, sausage and instant potatoes.

Spice extracts can be used in sprays, dips or surface coatings, and applied to comminuted poultry, seafood or meats before they are frozen, thereby inhibiting warmed-over flavors that develop after cooking and reheating. They also can be added in glazes and injection marinades for meats. For snack foods, these extracts can be added to frying oil or atomized on the surface of snacks. They can even be blended into dough, as they tend to be very heat stable and can withstand extrusion, spray-drying and baking processes.

Researchers at Texas A&M University, College Station, have investigated dried plums for their effect on controlling lipid oxidation in meat. Researchers identified that dried plums contain phenolic chlorogenic and neochlorogenic acids, which can hinder lipid oxidation in meat, thus preventing WOF from developing. They found that at 3% use levels, in both refrigerated and frozen precooked pork sausage, dried-plum puree is just as effective in preventing lipid oxidation as is a combination of BHA and BHT. Pork sausage was chosen for this study because of its high fat content and large percentage of unsaturated fatty acids.

Studies at the University of Zaragoza, Spain, have shown that adding ground peppers (both sweet and hot) to beef burgers can delay and significantly inhibit lipid oxidation, extending shelf life from four days to about 16 days. The researchers also looked at the effect of lycopene-rich tomato products, and while results showed that such tomato ingredients were not as effective as treatment with peppers, they too exerted an antioxidative effect, extending shelf life to between eight and 12 days.

Honey also provides benefits, with antioxidant content varying by nectar source. In general, the darker the honey’s color, the higher its antioxidant activity. Honey contains a number of compounds that possess antioxidative properties. These include, but are not limited to, alpha-tocopherol, ascorbic acid and beta-carotene.

Researchers at the University of Illinois, Urbana-Champaign, have shown that honey (5% by total weight) added to ground turkey slows down oxidation of lipids. A usage level of 5% was not enough to make the turkey taste sweet, but was enough to make a difference in reducing rancidity.

To reap the benefits of antioxidants, these active ingredients must be completely dispersed in the food system, and as early as possible during manufacturing.

“Antioxidants can protect fats or oils from oxidation but cannot rejuvenate already oxidized fats or oils,” comments Byrd. “To maximize the benefits of antioxidants they should be added as early as possible in the production process. However, food manufacturers must also be aware of processing steps that can destroy or remove antioxidants. For instance, propyl gallate breaks down when exposed to most baking temperatures, thus inactivating it.”

Order of addition is also very important. Some ingredients in a food system can interfere with antioxidant dispersion if added in the wrong order during mixing. For example, ingredients that bind water, which is often the vehicle for antioxidant dispersion, will prevent the antioxidant from being thoroughly dispersed in the food system.

Most “recognized” antioxidant ingredients are sold to food manufacturers in either a dry, powdered form, or dispersed in a solution. When purchased in powdered form, the food manufacturer usually adds antioxidants to a solvent or carrier. This ensures thorough dispersion in the food product, as usage levels tend to be quite low. Antioxidant solutions eliminate the dispersion step for manufacturers. Suppliers can also provide customized blends of antioxidant ingredients in the solution.

Antioxidants can be directly added to food systems, as in the case of fats, oils and salad dressings. They can be sprayed or atomized onto foods, like with nuts, cereals and spices.

Breakfast cereals, though typically low in fat, are very susceptible to oxidation because the little bit of fat that is present is usually highly unsaturated. Breakfast cereals also have a great deal of surface area. This increases exposure to oxygen, and thus increases the possibility of oxidation. It is very common to incorporate highly volatile antioxidants into the liners of cereal boxes. From here, the antioxidants volatize and evenly incorporate into the flake, puff, ring or crisp.

In addition to using ingredients with antioxidative properties, manufacturers can incorporate various packaging technologies (e.g., modified atmosphere, vacuum, oxygen scavengers, etc.) into their process. Regardless of the approach, formulators must keep fats from breaking down in the presence of oxygen in order to keep foods tasting great.

Donna Berry, president of Chicago-based Dairy & Food Communications, Inc., a network of professionals in business-to-business technical and trade communications, has been writing about product development and marketing for nine years. Prior to that, she worked for Kraft Foods in the natural-cheese division. She has a B.S. in food science from the University of Illinois in Urbana-Champaign. She can be reached at [email protected].

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