July 11, 2006
For much of history, highly saturated fats like lard and beef tallow were standard in the human diet and naturally evolved into common processed-foods ingredients. When research linked saturated fat intake with an increased risk for coronary heart disease (CHD), food processors increasingly began to use partially hydrogenated vegetable oils to produce foods with the sensory and stability qualities afforded by saturated fats. Unfortunately, the hydrogenation process yields trans fatty acids, which have been found to increase the risk of CHD and, some studies suggest, are even more harmful than saturated fats.
As reported in Shopping for Health 2004, a study conducted by the Food Marketing Institute, Washington, D.C., American food shoppers are trying harder to achieve good health through dietary changes, with 45% indicating that they are looking for more products without trans fatty acids. To help consumers make healthier food choices, FDA requires that food product labels must list the trans-fat content directly under saturated fat on the Nutrition Facts panel.
When work began to remove trans fats from processed foods, food designers quickly realized that formulating trans-free products was not simply a matter of exchanging one fat for another. Although technology has made significant progress, in certain applications, trans-free is accompanied by tradeoffs in quality, shelf life, price or nutrition. According to Frank Kincs, director R&D, Bunge Oils, Bradley, IL, Trans-fat replacements tend to be customer-specific. What works for one processor may not work for another. Still, the industry continues to widen the array of available alternatives.
According to the American Heart Associations (AHA) Heart Disease and Stroke Statistics2006 Update, cardiovascular disease continues to be the No. 1 killer in the United States. Dietary factors associated with an increased risk of CHD include consumption of foods high in saturated fat, cholesterol and trans fatty acids.
Most saturated fatty acids and dietary cholesterol raise levels of LDL (bad) cholesterol, a major risk factor in CHD. Some research suggests that stearic acid, a long-chain saturated fatty acid, has a neutral effect on serum cholesterol levels. Trans fatty acids not only increase LDL cholesterol, they also lower HDL (good) cholesterol, resulting in an undesirable rise in the ratio of total cholesterol to HDL cholesterol. An increase in this ratio is linked with a greater risk of CHD.
The FDA estimates the average daily intake of trans fat for U.S. consumers 20 years of age and older is approximately 5.8 grams, or 2.6% of calories. Saturated fat consumption is estimated to be 12% to 14% total calories. The AHAs Eating Plan for Healthy Americans recommends a saturated fat intake of 7% to 10% of total calories, up to 10% polyunsaturated fat and up to 15% monounsaturated fat. Saturated plus trans fatty acids should not exceed 10% total calories.
Hydrogenation is the process of adding hydrogen to unsaturated bonds on a fatty acid, thereby converting liquid oils into semi-solid/solid fats. Paul Sabatier, a French chemist noted for his research in catalysis, discovered the method in the early 1900s. He received the Nobel Prize in Chemistry in 1912, along with Victor Grignard, for his process of hydrogenating organic compounds using finely divided metals as a catalyst. Initially developed to harden soap, hydrogenation was adapted by American chemists to alter liquid oils for the food industry.
Fat and oil molecules typically consist of three fatty acids connected to a glycerol backbone. The many fatty acids that exist differ in length and in the number of double bonds (degree of unsaturation). The more saturated the fatty acid, the harder the fat and the higher its melting point at a specific temperature. Fat properties are also influenced by the geometric isomerism exhibited at a fatty acids double bond(s). Most naturally occurring unsaturated fatty acids are cis isomers, with the hydrogen atoms attached to the carbon atoms on the same side of the double bond. Trans isomers are characterized by hydrogen atoms on opposite sides of the double bond, which causes trans fatty acids to straighten out, much like the straight chain of a saturated fatty acid. Cis fatty acids bend at the double bond. A small amount of naturally occurring trans isomers are found, primarily in meat and dairy products, formed by the biological hydrogenation of polyunsaturated fatty acids in ruminant animals. The main source of trans fatty acids in the diet is partially hydrogenated vegetable oils.Hydrogenation, which both increases the degree of saturation and forms trans fatty acids, involves reacting hydrogen gas with oil at elevated temperature in the presence of a catalyst.
Hydrogenation occurs on the surface of the catalyst, explains Don Banks, president, Edible Oil Technology, Dallas. If there is sufficient hydrogen available when the double bond opens, hydrogen will be added. If not, when the molecule moves away from the catalyst, cis isomers may switch to trans isomers. The formation of straighter-chain saturated and trans fatty acids allows the fat molecules to fit closer together, increasing both the melting point and the solids content of the fat. However, its important to remember that if hydrogenated completely, all double bonds are eliminated, and the fat contains no trans fatty acids.
Hydrogenation increases the oxidative stability and alters the physical and functional properties of an oil. The double bonds of unsaturated fatty acids are highly reactive with oxygen; therefore decreasing the number of double bonds increases resistance to oxidation. By controlling the degree of hydrogenation, processors can produce fats that range from liquid oils to pourable and solid shortenings, each with specific physical properties. Attributes like melting point and solid fat index (SFI), the measure of a fats solid content at a given temperature, can be tailored to meet application requirements. Hydrogenation confers important functionalities, such as: oxidative and heat stability to frying oils, plasticity to bakery shortenings, smooth mouthfeel to chocolate substitutes, and desirable melt to table spreads. This translates into flavorful fried foods, tender baked goods, creamy confections and consistent margarines.
Partially hydrogenated fats enable the design of prepared foods with diverse end-product qualities, but without a high saturated fat content or increasing dietary cholesterol. Removing trans fatty acids presents technological and nutrition challenges. Technically, the dilemma centers on how to provide the functionalities of hydrogenated fats to foods without hydrogenating the fat. Nutritionally, there is some concern that trans-fats will be replaced with higher levels of saturated fatty acids. Several approaches can solve these challenges and some of the trade-offs associated with their use.
Alternate oils. While soybean oil has been the workhorse of the U.S. fat and oil industry, the trans-fat issue is encouraging the consideration of lesser-used oils, such as corn, cottonseed, high-oleic canola, sunflower and safflower, and rice bran. In general, these oils naturally possess heat and oxidative stability comparable to some partially hydrogenated oils. A few of these alternatives may impart a different, but not objectionable, flavor to end products than consumers are accustomed to with soy oil.
Traditional and biotechnological plant-breeding methods are being used to alter the fatty acid profile of some oilseeds to produce healthier, higher-stability oils with improved functionalities. For example, low-linolenic soybean oil contains less than 3% linolenic acid, as compared to about 8% in standard soybean oil. During hydrogenation, linolenic acid (three double bonds) is converted into more-stable linoleic (two double bonds) and oleic (one double bond) acids. Reducing the linolenic content in the seed increases the flavor stability of the oil by making the oil look and function more like a partially hydrogenated product, says Richard Galloway, consultant to the United Soybean Board, Chesterfield, MO.
Other seed modifications include midoleic (55% to 65% oleic acid)/lowlinolenic soybean oil for improved flavor and oxidative stability, and high-oleic canola oil (minimum 70% oleic) with good resistance to heat and oxidation.
In addition to being trans-free, many of these alternate oils have healthier fatty-acid profiles consisting of relatively low levels of saturates and high levels of monounsaturated fatty acids (MUFA), like oleic acid. Research indicates that oleic acid reduces serum cholesterol and LDL cholesterol levels, without affecting HDL cholesterol level. Oils with beneficial fatty-acid profiles include mid-oleic/low-linolenic soybean oil (15% saturates, minimum 55% oleic), high-oleic safflower oil (about 7% saturates, 78% MUFA) and high-oleic canola oil (7% saturates, minimum 70% oleic).
A drawback with lesser-used and higher-stability oils is that they are often higher priced with limited supply. This generally changes as demand increases. An oil is considered in full commercial production, and is generally more competitively priced, when annual output reaches more than one billion pounds, states Banks. We are approaching that point with low-linolenic soy, while midoleic soy will reach commercial production in about two years.
Blending. Typically used to produce trans-free margarines and shortenings, blending involves combining fully hydrogenatedand therefore trans-freevegetable oils and/or highly saturated trans-free tropical oils with regular or higher-stability oils. A blends functional properties depend on the saturated fatty-acid content. Processors can make trans-free blends that do not exceed the initial level of trans plus saturates; however, some applications may need to trade a higher amount of saturates for the required functionalities. Depending on endproduct requirements, blends can be made with a lightly hydrogenated, low-trans fat. This can meet regulations, because FDA allows a label declaration of zero trans fat for products containing less than 0.5 grams trans per serving.
Interesterification. Another method for producing solid fats, interesterification entails blending a liquid oil and a fully hydrogenated fat, cleaving off the fatty acids from the glycerol backbones and then randomly reforming the fatty acids into triglycerides. Rearranging the fatty acids modifies the fats functionalities, making it capable of replacing trans-containing partially hydrogenated fats. Containing up to 3.5% trans fatty acids, Some interesterified fats with increased levels of polyunsaturated fatty acids can have less oxidative stability than their partially hydrogenated counterparts; however, this trade-off can be reduced through the use of antioxidants and/or improved packaging, says Tom Tiffany, manager, food oils applications R&D,ADM, Decatur, IL.
Expeller-pressed oil. Oil is typically removed from the seed by chemical solvent extraction, a highly efficient process that can remove over 99% of the oil from the seed. All-natural expeller extraction, one of the oldest known processes used to remove oil from oilseeds, removes about 92% of the oil from the seed. Trans-free with the stability of some partially hydrogenated oils, expeller-pressed oil retains the antioxidants naturally present in the soybean, plus compounds are created during processing that have synergistic antioxidant properties, says Rob Kirby, president, Nexcel Natural Ingredients, Division of Spectrum Foods, Inc., Springfield, IL. The antioxidants contribute to the oils flavor and oxidative stability, and help maintain end-product shelf life. Typical of specialty products, expeller-pressed oil is higher-priced than commodity oils.
Emulsifiers or gelling agents. While trans-free alternatives can provide a solid-fat content similar to partially hydrogenated products, they do not always deliver the desired end-product attributes and may crystallize slower, which reduces production capacity. We have patented an emulsifier and liquid oil system that mimics the functionality of partially hydrogenated shortening, says Terese ONeill, regional marketing and business director, Danisco, New Century, KS. The system does not increase solids, rather, the emulsifier blend enhances the oil structure by forming an alpha-gel which provides the required structure and mouthfeel.
Ranging from light-duty sautéing to continuous, heavy-duty foodservice cooking, frying operations require oils with varying degrees of flavor, oxidative and heat stability. The wide variety of trans-free oils, available with various fatty-acid profiles and functionalities, allows the design of trans-free fried products with specific nutritional, sensory and shelf-life attributes.
When evaluating new fry oils, product designers need to consider their smoke, flash and fire points, standard measures of the oils thermal stability when heated in contact with air. While the degree of unsaturation of an oil has little, if any, effect on these characteristics, oils with low-molecular-weight fatty acids, such as coconut oil, will have lower smoke, flash and fire points than other fats with a comparable freefatty- acid content. Ideally, a frying fat should be stable at high temperatures, have a smoke point above 200°C and a flash point above 315°C.
The new higher-stability soybean and canola oil varieties are proving to be effective trans-free replacements for partially hydrogenated oils, offering healthier fatty- acid profiles and a range of stability options. According to Banks, Low-linolenic soybean oil can replace partially hydrogenated oil in light-duty frying applications. It has significantly improved flavor stability and does not develop objectionable grassy notes that can occur in regular soybean oil during oxidation. Mid-oleic soy has good oxidative stability and is a suitable replacement for medium-duty partially hydrogenated frying oils.
High-oleic canola possesses the heat and oxidative stability needed for heavy-duty frying. Studies indicate that foods fried in high-oleic canola oil have a cleaner taste, crispier texture and longer end-product shelf life than products fried in a partially hydrogenated oil. Plus, high-oleic canola oil exhibits a longer fry life than a typical partially hydrogenated soybean oil, offering an economic advantage. Processors can customize high-stability oils to meet end-product requirements. We offer a blend of high-oleic canola oil and corn oil, which can satisfy many processors need for an economical, highly-stable fry oil with a unique flavor profile, says Kincs.
In addition to providing functional and nutritional benefits, lesser-used trans-free oil varieties can promote product differentiation. For example, high-oleic sunflower (9% saturates, minimum 80% oleic) and high-oleic safflower (7% saturates, minimum 75% oleic) oils have good fry stability, plus they have a favorable image with consumers, says John Gyulai, president, Oilseeds International, San Francisco. Cottonseed oil (27% saturates, 19% MUFA, trace linolenic and 54% linoleic), which has a bland, slightly nutty taste, was the original American vegetable oil and has been used for years for cooking and frying. Corn oil (13% saturates, 29% MUFA, 1% linolenic and 57% linoleic) is a useful alternative to lightly hydrogenated soybean oil, suitable for light-duty frying. Peanut oil (19% saturates, 48% MUFA, trace linolenic and 33% linoleic) offers heavy-duty fry stability as well as a distinctive nutty flavor.
While fatty-acid composition is key to the stability of many oils, rice bran oil (about 17% saturates, 43% MUFA, 1% linolenic and 39% linoleic) and expeller- pressed oil have the added benefit of naturally present antioxidants. Our high-stability Oryzan rice bran oil contains approximately 1% of the powerful natural antioxidant oryzanol, states Gyulai. During frying, oryzanol does not dissipate as quickly as added synthetic antioxidants, which tend to flash off early. This gives the oil a long fry life and helps to extend end-product shelf life. In a sensory test, panelists felt that French fries prepared in rice bran oil were less greasy, with better true-potato flavor than those fried in soybean oil. Oryzan rice bran oil can be used alone or blended with other oils for improved frying performance without hydrogenation. Expeller-pressed oil has also been shown to enhance overall product quality. Tests indicate that our expeller-pressed oil matched the fry life of partially hydrogenated soybean oil while producing end products with higher taste and color scores, says Kirby.
Spraying on stability
Spray oils are used as a pan-release agent and on products like snacks and cereals to provide a moisture barrier, improve appearance, adhere seasonings and carry flavors. The fats SFI profile, and flavor, mouthfeel and appearance on the finished product are important selection factors
Partially hydrogenated oils have often been used for their resistance to oxidation, ability to withstand elevated application temperatures, and good mouthfeel. Various trans-free oils can supply these functionalities along with a bland to mild flavor that will not interfere with a products taste profile. Options range from high-oleic canola, safflower and sunflower oils to rice bran and expeller-pressed oils.
Emulsifiers can improve the effectiveness of trans-free spray oils. Spraying a product like crackers with a non-hydrogenated oil typically causes an oily mouthfeel, less flavor release and some oxidation issues, notes ONeill. Adding emulsifiers to an oil, including a non-hydrogenated one, speeds up fat crystallization during cooling, improves flavor release and prevents oiling off. Higher-stability oils can be used to minimize oxidation.
A solid look at shortenings
The baking industry has relied on partially hydrogenated fats to supply end-product qualities like tender pastry structure, good cake volume and rich-tasting cream fillings. Transfatty acids give shortening a wide range of plasticity, which allows one shortening to be used in numerous applications, explains Banks. Transfree shortenings have narrower functionality and tend to be more application-specific. To achieve the required shortening properties, trans-fatty acids are replaced with saturated fatty acids, which can impact the end products nutrition profile. Blending and interesterification are being used to produce low/no trans shortenings, margarines and other table spreads.
With a wide range of hard fats and liquid oils to choose from, blends can be customized to meet specific functional and nutrition requirements. For example, a roll-in bakery shortening might use a fully hydrogenated soybean oil to provide the saturates needed for a specific melting point and SFI/SFC, and a mid-oleic/low-linolenic oil to minimize any increase in saturated fatty acid level. For a trans-free cookie cream filling with a smooth, non-waxy mouthfeel, A vegetable oil/lauric fat blend can provide the required physical properties, but at a lower level of saturates than if a lauric fat was used alone to replace the partially hydrogenated vegetable oil, says Tiffany.
According to Kincs, Traditional partially hydrogenated all-purpose bakery shortening contains about 20% to 25% saturates and 25% trans fatty acids for a total 45% to 50% saturates plus trans. Using a special process, we produce a shortening from soybean and cottonseed oils that has less than 5% trans and a saturate level similar to traditional all-purpose shortening.
Applications include cookies, pie crust and biscuits. We also use this low-trans shortening as a base for other bakery fats, such as our all-purpose bakery margarine for products like Danish and coffee cake. Combining the shortening with emulsifiers results in a cake and icing fat with required whipping and moisture-holding properties. Interesterification produces shortenings and margarines with physical properties that are not possible by simply blending oil and fat fractions. For example, interesterifying with oils containing palmitic acid yields more functionality than achieved by blending, facilitating production of a beta-prime stable shortening.
Additionally, the type of feedstock used in interesterification can improve a fats nutritional quality. Tiffany notes, Our enzymatically interesterified soy-based shortenings contain less than 3.5% trans fatty acids, with 40% total saturates plus trans. These domestic- oil-based fats have increased levels of linolenic and linoleic fatty acids, resulting in a higher level of polyunsaturated fatty acids compared to partially hydrogenated soy. And by using a fully hydrogenated soybean oil, which consists of about 87% stearic acid, the type of saturates is improved. (As noted earlier, studies suggest that stearic acid has a neutral effect on blood cholesterol level.)
Palm fruit oil, a trans-free semi-solid fat at room temperature, is increasingly being used in blended and interesterified shortenings intended as substitutes for hydrogenated fats. Consisting of about 50% saturated fat and 50% unsaturated fat, palm fruit oil differs from palm kernel oil, which contains about 85% saturated fatty acids. Palm fruit oil is often fractionated into palm olein, which is more liquid and high in monounsaturates, and palm stearin, a more-solid fraction that is frequently used as the hard fat component in trans-free solid fats. In margarines and shortenings, the fatty acids in palm oil crystallize in the stable beta-prime form, which is responsible for a smooth texture and optimum mixing and creaming ability. Palm fruit oil is rich in antioxidants, including betacarotene (as in red palm oil), tocopherols and tocotrienols, states Salleh Kassim, executive director, American Palm Oil Council, Torrance, CA. Studies indicate that palm oil/olein is not a risk factor for coronary heart disease. Indeed, when included in a diet that adheres to the AHA recommended fatty-acid blend, including almost 50% palm oil/olein beneficially modulates the LDL/HDL cholesterol lipoprotein ratio, which is an acknowledged indicator for assessing coronary heart disease risk.
Trans-free baked goods, such as cookies, pie crusts and tortillas, can also be achieved by formulating with liquid oil instead of a shortening. In these instances, emulsifiers are useful for improving end-product quality. Our emulsifier system forms a crystalline structure with the oil that mimics the properties supplied by a partially hydrogenated fat, says ONeill. When included in a cookie made with a transfree, low-saturate oil, our emulsifier provides good structure and prevents an oily mouthfeel.
Chocolate receives its rich character from cocoa butter, which contains about 35% stearic acid and 25% palmitic acid for a total of 60% saturated fatty acids. However, for many confectionery coatings and similar products, manufacturers make chocolatey compound coatings using cocoa-butter replacers. These have typically been made with partially hydrogenated soybean and cottonseed oils and can contain up to 60% trans fatty acids and 20% to 30% saturates, says Tiffany. Partial hydrogenation provides key functionalities, such as stability, melt behavior, gloss, snap and texture.
For trans-free confectioneries, many processors are switching to cocoa-butter substitutes, which are based on tropical oils like palm and coconut oil (lauric fats). Interesterifying palm olein produces a cocoa butter substitute with the snap, crunch and melt-in-the mouth sensation of chocolate. A blend of transfree palm fruit oil and palm kernel oil fractions can yield a compound coating with physical properties similar to chocolate. All fats crystallize differently, and processing conditions, like the cooling temperature, may need adjustment to produce the desired end product, notes Kincs.
While significant progress has been made on trans replacement, work continues to provide food designers with additional options.
Researchers are examining hydrogenation under super critical conditions as a method of producing partially hydrogenated oils without forming trans fatty acids. With this system, an unlimited amount of hydrogen would be available at the catalyst to allow immediate saturation and prevent the formation of trans isomers, says Banks.
Efforts are continuing to modify oilseed traits, such as decreasing the saturates in soybeans to less than 7% while keeping linolenic low and maximizing oleic, says Galloway. Depending on the amount of fat in an end product, this low saturate level could have favorable labeling ramifications, since FDA allows products that contain less than 0.5 grams saturated fat per serving to be labeled as zero grams saturated fat.
Another objective is more-economical trans-free options. Palm oil and its derived fractions tend to crystallize slower than soy oil products, reducing the production throughput of palm-based shortenings, says ONeill. We are working on an emulsifier system that will minimize this effect while also improving the eating quality of end products by decreasing oiling-out and enhancing texture.
Gyulai adds, The food ingredient industry has come a long way in making changes in fats for processed foods. And there are more changes to come. The next big target will be the food service industry, where there is growing demand for labeling and declaring the nutrition content of restaurant foods.
Freelance technical writer Elaine Knehr holds a B.S. in Food Technology and an M.S. in Business Administration. Her 10 years of experience in product development covers a wide range of food products.
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