Issue Date: May 31, 2010
Sowing The Seeds Of Oil Customization
Food labels and ads proclaim "zero trans fats" and "naturally rich in heart-healthy oils." Media outlets report that several cities ban restaurants from using common cooking oils. And news talk shows spur lively discussions about the pros and cons of genetically modified soybeans and other crops.
Nowadays, it's hard to dodge the nearly constant flow of information about agricultural science and seed oils. The steady stream of information is motivating a thriving research thrust that's focused on producing oilseeds such as soy, canola, and sunflower with customized chemical compositions.
Heightened public awareness of both good and bad health consequences of diets rich in some types of oils is one of the key drivers in the push to modify seed oil compositions. For food-related applications, scientists could turn to chemical processing technology to alter conventional edible oils into healthier alternatives. But by using biological know-how, "we can get the plants to do it efficiently by themselves," says Federico A. Tripodi, the omega-3 program director at agriculture technology company Monsanto.
Improving foods to promote good health isn't the only goal in this arena. Scientists such as Jan G. Jaworski, vice president for research at the Donald Danforth Plant Science Center, in St. Louis, see important opportunities for using oilseeds "as factories for producing renewable fuels and materials." Jaworski's aim is to capitalize on those opportunities by engineering seeds too produce industrial quantities of customized oil. Achieving that goal could help society shift its dependence from petrochemicals to plant-based oleochemicals.
Industrial-scale processes for modifying oils for use in food date back more than a century. Following chemistry Nobel Laureate Paul Sabatier's work on catalytic hydrogenation of gas-phase organic compounds, German chemist Wilhelm Normann developed a method in the early 1900s for hydrogenating liquid oils. The process was used to harden and stabilize fats. Soon after, it was also used to produce Crisco vegetable shortening, now a nearly 100-year-old product.
The need for hydrogenating oils stems from their chemical compositions. Seed oils contain a mixture of saturated and unsaturated fatty acids. The saturated compounds are relatively stable, but unsaturated compounds—in particular, ones with multiple carbon-carbon double bonds—can undergo unwanted reactions. Hydrogenation can help address this problem by boosting saturation.
Common soybean oil consists of approximately 15% saturated fatty acids, such as palmitic acid, also known as hexadecanoic acid, CH3(CH2)14COOH. The oil also contains roughly 24% oleic acid, a C18 compound with unsaturation at one bond; 54% linoleic acid, a doubly unsaturated C18 compound; and about 7% α-linolenic acid, an 18-carbon fatty acid with three olefin groups.
Containing more than 60% polyunsaturated compounds, soybean oil and other oils with similar compositions are highly susceptible to oxidation reactions when used at high temperature, for example for frying or baking. Those reactions cause the oils to decompose and become rancid, according to DuPont research scientist Susan Knowlton. The reactions can also cause the oils to darken, become viscous, and leave a polymer coating on frying equipment, she says, all of which can impart a bad taste to foods cooked in or made with those oils.
Hydrogenation reduces the number of reactive unsaturations and thereby stabilizes oils, thereby extending their shelf and fryer lives and preserving good flavor in foods made with those oils. If the process is carried out only partially, then an oil's properties can be modified such that the product's melting point and consistency resemble that of butter, which is ideal for many applications, according to Fred J. Eller, a Department of Agriculture research scientist in Peoria, Ill.
It turns out, however, that during partial hydrogenation of oils, unsaturated fatty acids can undergo unwanted isomerization reactions that convert the acids' alkene functional groups from their naturally occurring cis configuration to the trans configuration. As Eller explains, that conversion happens by way of a series of basic steps that include reversible addition of a hydrogen atom to one of the carbon atoms in an alkene group. After that step, the molecule can then rotate about the newly formed C–C single bond, lose the hydrogen atom, and re-form the C=C double bond in the energetically favored trans configuration.
The outcome is that the industrially important partial hydrogenation process, as implemented for decades, yields oil products that are rich in harmful trans fatty acids. By now, these compounds have been widely implicated for their roles in increasing rates of human cardiovascular disease and diabetes, among other ill effects. In response to numerous health studies, the Food & Drug Administration requires manufacturers to list on food labels the quantities of trans fats present in their products. And New York City, Boston, Philadelphia, and other cities in the U.S. and abroad have gone beyond mandatory food labeling and have passed legislation banning restaurants and other eateries from using oils containing trans fatty acids in food preparation.
Seeing the writing on the wall more than a decade ago, agricultural research organizations such as Monsanto, DuPont's Pioneer Hi-Bred, and Dow AgroSciences undertook projects to produce oilseed plant varieties that deliver healthier oils yet maintain properties of partially hydrogenated oils important to the food industry.
Working with oilseed processor Bunge North America, Pioneer used traditional plant-breeding methods to develop a line of low α-linolenic acid soybeans, which are sold under the trade name Treus. The company showed that for some applications—for example, light frying—the reduced concentration of the polyolefin α-linolenic acid (3% compared with 7–8% in traditional soybean oil) eliminates the need for partially hydrogenating the oil and hence avoids production of trans fats. Similarly low α-linolenic acid levels (3%) characterize oils produced from Monsanto's Vistive soybeans. Those oils are widely used by KFC, Kellogg's, and other food processors, according to company press releases.
Reduced α-linolenic acid oils represent an improvement over commodity oils, but the story doesn't end there. "The food industry really wants oils that are much higher in monounsaturated fats, because they do not raise cholesterol levels and are therefore considered healthful fats," says David M. Stark, Monsanto vice president for consumer traits. But the oils also need to be stable to provide long shelf and fryer life, he adds, which means simultaneously reducing the levels of polyunsaturation.
To customize seeds so they yield that complex combination of oil traits, researchers have turned to genetic engineering. For example, scientists at Pioneer developed methods to block expression of certain soybean enzymes in a way that leads to the seeds' buildup of oleic acid and at the same time a reduction of linoleic and α-linolenic acids, according to Knowlton. Pioneer's Plenish brand of soybean oil, which the company anticipates commercializing in the U.S. later this year, boasts more than 75% oleic acid—more than three times the level found in typical soybean oil.
Likewise, Monsanto has used genetic modification to boost oleic acid to the 75% level in its soon-to-be-commercialized line of Vistive Gold soybeans. Stark points out that the increase in oleic acid is accompanied by a decrease in linoleic acid from the mid-50% range to roughly 17% and a decrease in α-linolenic acid from 7–8% to approximately 2.5%. In addition, unlike corn oil, olive oil, and commodity soybean oil, all of which typically contain some 15% saturated fat, these newer lines of soybeans contain only about 7% saturated fat. Like trans fatty acids, saturated fats such as palmitic acid (hexadecanoic acid) and stearic acid (octadecanoic acid) have been identified as culprits in increased risk for heart disease.
Dow AgroSciences capitalized on canola and sunflower seeds' naturally occurring low levels of saturated fatty acids (approximately 7%) to develop seeds with an oil profile that's customized for today's health-conscious food-service industry. Similar to today's "high tech" soybeans, these new lines of canola and sunflower seeds, which were produced via conventional plant-breeding methods, yield in excess of 70% oleic acid and less than 3% α-linolenic acid. Those values contrast with roughly 62% and 9%, respectively, in commodity canola oil, according to Erin M. Hull, brand manager for the company's omega-9 oils. (The "omega-x" name indicates the position of the alkene group closest to the end of the fatty acid's alkyl chain.)
Hull notes that Dow is now working to develop sunflower oil low enough in saturated fat to qualify for the "0 saturated fat" food label designation. In addition, the company has teamed up with Martek Biosciences to genetically modify canola seeds to produce docosahexaenoic acid (DHA), a 22-carbon omega-3 fatty acid found in oils from salmon and other fish (C&EN, Aug. 11, 2008, page 39). Such compounds have been shown to play a role in brain and eye development and to have other health benefits.
Monsanto researchers are also working on plant-based sources of nutritious fish-oil components. Their strategy is based on preparing genetically altered soybeans that produce stearidonic acid (SDA), an 18-carbon omega-3 fatty acid that serves as a precursor in humans to larger omega-3 compounds such as DHA, according to Tripodi. FDA recently classified Monsanto's SDA soybeans as generally recognized as safe—"a significant milestone," Tripodi says, "indicating that we have safely modified the oil's fatty acid profile without any unintended consequences."
As a result, manufacturers have begun testing the SDA soy oil in granola bars, yogurt smoothies, and other foods. Consumer tests (such as one this C&EN reporter participated in) show that the SDA-soy-oil products look and taste perfectly fine.
Although some researchers customize oilseeds for food applications, Jaworski and his Danforth Center coworkers are altering plant genes, such as the ones in Camelina sativa plants, to make biodiesel and jet fuels. C. sativa is grown only in small scale today, Jaworski says, but he favors studying it because it grows quickly, does so on land of marginal farming value, and requires little fertilizer and water. As an example of C. sativa's potential value as a genetically engineered fuel source, Jaworksi points out that ordinary C. sativa oil contains nearly 55% polyunsaturated compounds and just 8% monounsaturated ones, which would limit the fuel's stability and hence storage life. By altering just one gene, his group reduced the polyunsaturated fats to 9% and boosted the level of the key monounsaturated compound to more than 55%.
From soy to sunflower and canola to C. sativa, oilseed research is progressing quickly. Continued advances in breeding, genetic engineering, and chemistry are sure to continue to boost the healthfulness of farm-grown, custom-made seed-based products.
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