The Two Faces of Edible Soy: Vegetable Oil and Protein

When one thinks of soy, the traditional Asian soyfoods – tofu, miso, natto, tempeh – most likely come to mind. While these foods play key roles in Asian cuisines and increasingly in non-Asian cuisines, they account for only a small percentage of the soybeans produced worldwide.

About 600,000 US soybean farmers produce nearly four billion bushels of soybeans per year, which is equivalent to over 800 billion pounds.1 The US crop represents about 40% of the world’s soybean production. Most of the soybeans-- about 85% -- are processed into meal (protein) and oil. The former is used primarily as animal feed, whereas the latter has become the most widely consumed vegetable oil in the world. In fact, soybean oil accounts for about 7% of the caloric intake of Americans and contributes over 40% of the US intake of both essential fatty acids.2

Soybean oil is used extensively by the food industry, although most oil is purchased directly by consumers. However, since soybean oil is typically marketed as 100% vegetable oil, many consumers may not recognize they are actually consuming soy. If not being exposed to soy via soybean oil, for many consumers exposure to soy will occur in the form of lecithin. In this country, soybean oil is the primary source of this emulsifier which is widely used by the food industry and which has also been studied for a number of health benefits especially in the areas of cognitive function3-6 and inflammatory-related diseases.7,8 Soybean oil is also a rich source of vitamins E and K.9 The predominate form of vitamin E in soybean is gamma-tocopherol,10 which has been less well studied than alpha-tocopherol but which may have some desirable health attributes not shared with alpha-tocopherol.11,12

Soybean oil has a very heart-healthy fatty acid profile as it is comprised of almost 90% unsaturated fatty acids, about two-thirds of which is linoleic acid.13 Nevertheless, new varieties of soy oil are being developed. For example, as discussed by Wang and MacDonald elsewhere in this issue, high-oleic soybean oil was developed in response to the almost complete removal of trans fatty acids and partially hydrogenated oils (PHO) from the US food supply. PHOs were designed to be healthful alternatives to saturated sources of fat, such as lard and butter, but were later shown to have adverse effects on blood lipids at modest levels of intake. Alternatives are needed to replace the functional properties provided by trans-fat sought by the food industry. New oils with the desired properties can also be created by interesterification and blending.

Many consumers who aren’t directly consuming soyfoods are still meeting part of their protein needs from soy protein. A small percentage of meal that is left after removing the oil is used to make several soy protein products including soy protein isolate, soy protein concentrate and soy flour. By definition, these products are approximately 90%, 70% and 50% protein, respectively.

As discussed by Riaz, also in this issue, these soy products have a variety of functional properties that account for why small amounts are added to literally hundreds of commonly consumed foods. In addition, because consumers are looking to increase their protein intake, soy protein, especially in the form of soy protein isolate, is being added to foods to increase their overall content of this macronutrient. Finally, various forms of soy protein are ideal base ingredients for meat analogs such as burgers, sausages and chicken nuggets because soy is a high-quality protein and has a largely neutral flavor profile that allows food scientists to develop products that taste similar to their meat-containing counterparts.

In conclusion, soybeans are important, sustainable, components of the food supply because they provide a wide variety of healthful oils that can be tailored for their nutritional and functional properties, are sources of high quality protein,14 and are ideal for the formulation of a plethora of nutrient dense and affordable foods.

References

1.  Annual Crop Production: 14.2 Billion Bushels of Corn, 3.97 Billion Bushels of Soybeans. http://www.agweb.com/article/annual-crop-production-142-billion-bushels-.... Accessed May 16, 2016.
2.  Blasbalg TL, Hibbeln JR, Ramsden CE, Majchrzak SF, Rawlings RR. Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century. The American journal of clinical nutrition. May 2011;93(5):950-962.
3.  Richter Y, Herzog Y, Lifshitz Y, Hayun R, Zchut S. The effect of soybean-derived phosphatidylserine on cognitive performance in elderly with subjective memory complaints: a pilot study. Clinical interventions in aging. 2013;8:557-563.
4.  Schreiber S, Kampf-Sherf O, Gorfine M, Kelly D, Oppenheim Y, Lerer B. An open trial of plant-source derived phosphatydilserine for treatment of age-related cognitive decline. The Israel journal of psychiatry and related sciences. 2000;37(4):302-307.
5.  Kato-Kataoka A, Sakai M, Ebina R, Nonaka C, Asano T, Miyamori T. Soybean-derived phosphatidylserine improves memory function of the elderly Japanese subjects with memory complaints. Journal of clinical biochemistry and nutrition. Nov 2010;47(3):246-255.
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9.  Kamao M, Suhara Y, Tsugawa N, et al. Vitamin K content of foods and dietary vitamin K intake in Japanese young women. J Nutr Sci Vitaminol (Tokyo). Dec 2007;53(6):464-470.
10.  Guzman GJ, Murphy PA. Tocopherols of soybean seeds and soybean curd (tofu). Journal of agricultural and food chemistry. 1986;34:791-795.
11.  Cooney RV, Franke AA, Harwood PJ, Hatch-Pigott V, Custer LJ, Mordan LJ. Gamma-tocopherol detoxification of nitrogen dioxide: superiority to alpha-tocopherol. Proc Natl Acad Sci U S A. Mar 1 1993;90(5):1771-1775.
12.  Cooney RV, Harwood PJ, Franke AA, et al. Products of gamma-tocopherol reaction with NO2 and their formation in rat insulinoma (RINm5F) cells. Free Radic Biol Med. Sep 1995;19(3):259-269.
13.  Slavin M, Kenworthy W, Yu LL. Antioxidant properties, phytochemical composition, and antiproliferative activity of Maryland-grown soybeans with colored seed coats. Journal of agricultural and food chemistry. Dec 9 2009;57(23):11174-11185.
14.  Hughes GJ, Ryan DJ, Mukherjea R, Schasteen CS. Protein digestibility-corrected amino acid scores (PDCAAS) for soy protein isolates and concentrate: Criteria for evaluation. Journal of agricultural and food chemistry. Dec 14 2011;59(23):12707-12712.