Soy Oil Advances with Food Applications Through Emerging Technologies

Soybean oil was introduced to the American consumer during World War II when domestic and imported sources of fat became limited. Because of its versatility for home and commercial food preparation, soybean oil grew to be the major contributor of both essential fatty acids to the US diet.

The richest dietary sources of n-3 fatty acids are fish and fish oils, and flaxseed. Soybean and canola oil contain alpha-linolenic acid (ALA) (Table 1) in amounts higher than corn, olive or palm oil. The endogenous conversion of ALA to the longer chain omega-3 fatty acid, eicosapentanoic acid (EPA) is, however, inefficient. Therefore substantial research has been undertaken to develop new varieties of soybean that contain fatty acids which are more likely to be converted to health-promoting fatty acids such as EPA.

The result has been a soybean oil that contains 18-20% of the omega-3 fatty stearidonic acid (SDA). Not only is this oil about 3x higher in omega-3 fatty acids than conventional soybean oil but SDA is more efficiently converted by the human body to EPA than ALA.1,2 The FDA has approved the use of SDA soybean oil and it is currently being developed for commercial scale production.3

Full or partial hydrogenation was developed in 1911 with the commercialization of Crisco, and became commonly used during the 1950s as a means to modify soybean and other vegetable oils to generate shortening and margarines to replace solid fats such as lard and butter. Concerns about saturated fats and cholesterol led nutritionists and public health authorities to recommend expanded use of margarines and shortenings and food manufacturers were under great pressure to eliminate animal fats from their products. Partially hydrogenated vegetable oils (PHOs) provided the functionality and product quality that food manufacturers needed in addition to being lower in saturated fat and free of cholesterol. Consequently, PHOs became widely used. The purpose of hydrogenation is to reduce the number of double bonds so the oil becomes more solid at room temperature and to increase oxidative stability. However, a negative consequence of the process is that some of the naturally occurring cis-double bonds are changed to the trans configuration. Although not recognized at the time, the unusual confirmation of trans-fats causes them to have adverse effects on blood lipids by increasing LDL-cholesterol and decreasing HDL-cholesterol, which are known risk factors for heart disease and atherosclerosis.4

Rising concerns about the health effects of trans-fats led the FDA to require them to be listed on the Nutrition Facts panel in 2003. Because PHO are a source of trans-fats, the FDA in 2015 determined that they should be removed from the Generally Recognized as Safe list and required food manufacturers to reformulate their products without PHO by 2018. Hence, efforts to eliminate trans-fats and to find replacement for PHO have been ongoing for several years.

Food scientists have been creative in developing ways to modify oils to achieve useful liquid-solid ratios without generation of trans-fats. The inter-esterification reaction (mostly catalyzed by enzymes) uses liquid oil and a saturated fat source to redistribute fatty acids in the triglyceride structure to make the product more solid. A saturated fraction of palm oil (palm stearin) or palm kernel oil can also be modified using this approach to produce a solid fat that contains zero-trans.

Fractionation is another tool that physically separates an oil into a more saturated stearin (solid) and a less saturated olein (liquid) fraction. The stearin fraction can then be blended with soybean oil to produce a semi-solid fat without trans-fats, making it suitable for a wide range of food applications. Another novel technology for converting liquid oil to solid or semi-solid fat is the creation of an oleogel. A gelator, such as a cellulose-based compound or plant wax, can be added to soybean oil to form a fat that has similar structural and mechanical properties as that of fat made using partial hydrogenation.5

Finally, the development of a high-oleic soybean variety which has a reduced saturated fat content and three times the oleic acid content of conventional soybean oil has potential to replace PHO especially for frying. High oleic soybean oil may also be used in blending and inter-esterification for making margarines and shortenings that are trans-free.6 It is projected that 9.3 billion pounds of high oleic soybean oil will be available by 2024.7

The future of soybean oil for food manufacturing and home food preparation continues to be bright as new varieties with health-promoting benefits and food applications are being developed, and novel ways to modify fats and oils are created.

Table 1. Typical fatty acid composition of oil (%)

1. Pelliccia, F., Marazzi, G., Greco, C., Franzoni, F., Speziale, G., and Guadio, C. 2013. Current evidence and future perspectives on n-3 PUFAs. Int. J. Cardiol. 170:S3-S7.

About the Authors

Tong Wang, PhD, is a professor at Iowa State University. She has research and teaching expertise on lipid chemistry and novel fat and oil processing and application technologies.

Ruth MacDonald, PhD, is a professor at Iowa State University and the Chair of the department. She has research and teaching expertise in human nutrition and food and sustainable agriculture.

References

1.  Lemke, S.L., Vicini, J. L., Su, H., Goldstein, D.A., Nemeth, M.A., Krul, E.S., and Harris, W.S. 2010. Dietary intake of stearidonic acid–enriched soybean oil increases the omega-3 index: randomized, double-blind clinical study of efficacy and safety, Am J Clin Nutr 92: 766-775.
2. Harris, W.S., Lemke, S.L., Hansen, S.N., Goldstein, D.A., DiRienzo, M.A., Su, H., Nemeth, M.A., Taylor, M.L. 2008. Stearidonic acid-enriched soybean oil increased the Omega-3 Index, an emerging cardiovascular risk marker. Lipids 43: 805-811.
3. Monsanto: Stearidonic Acid Soybean Oil. Accessed June, 2016.
4. Hammad, S., Pu, S., and Jones, P.J. 2016. Current evidence supporting the link between dietary fatty acids and cardiovascular disease. Lipids 51:507-517.
5. Wang, F.C., Gravelle, A.J., Blake, A.I., and Marangoni, A.G. 2016. Novel trans fat replacement strategies. Current Opinion in Food Science 7: 27–34.
6. AOCS, 2016. Innovative Alternatives for Hard Fats and High Stability Oils in the Food Industry. AOCS Annual meeting & Expo, May 2, 2016, Salt Lake City.
7. Qualisoy: High Stability Fats & Oils. Accessed June, 2016 https://www.qualisoy.com/food-industry-solutions/high-oleic-soybean-oil