Fatty acid composition soybean

Lipids. Representative fatty acid compositions of the unprocessed triglyceride oils found in the four oilseeds are given in Table 4 (see Fats and FATTY oils). Cottonseed, peanut, and sundower oils are classified as oleic—linoleic acid oils because of the high (>50%) content of these fatty acids. Although the oleic and linoleic acid content of soybean oils is high, it is distinguished from the others by a content of 4—10% of linolenic acid, and hence is called a linolenic acid oil. 

Identification Unhydrogenated Soybean Oil exhibits the following composition profile of fatty acids determined as directed under Fatty Acid Composition, Appendix VII ... 

Seedfats are characterized by low contents of saturated fatty acids. They contain palmitic, oleic, linoleic, and linolenic acids. Sometimes unusual fatty acids may be present, such as erucic acid in rapeseed oil. Recent developments in plant breeding have made it possible to change the fatty acid composition of seed oils dramatically. Rapeseed oil in which the erucic acid has been replaced by oleic acid is known as canola oil. Low linolenic acid soybean oil can be obtained, as... 

Soybeans are comprised of (w/w), 40% protein, 30% carbohydrates, and 20% oil (5, 4). Currently, about 95% of soy protein is used in feed and 4% in food (for human consumption) applications. On the other hand, about 94% of soybean oil is used in food and only about 4% in industrial applications. Soybean oil is a triglyceride, which is a triester of glycerol and three fatty acids. The main fatty acid composition of soybean oil is (w/w) linoleic (54), oleic (23), and linolenic (8), (5). These fatty acids contain 1, 2, and 3 double bonds, respectively, in their hydrocarbon chains. These double bonds or unsaturations are reactive sites and allow for the development of soybean oil for various applications. 

Attempts are being made to modify the fatty acid composition of soybean oil to enhance its usefulness. Oils with less or more saturated acid, with less linolenic acid, and with high levels of oleic acid are in various stages of development (55). 

Finally, genes required for particular aspects of fatty acid and triacylglycerol biosynthesis can be identified in appropriate sources, cloned, and transferred to other plants. Rapeseed has proved to be particularly flexible in this respect, and its fatty acid composition has been modified in several ways, some of which have now reached or are very close to commercial application (Section 9.4). Genetic modification procedures are also applied to soybean and other oilseed crops. 

TABLE 12. Fatty Acid Composition of Commodity Soybean Oii and Some Geneticaiiy Modified Oiis Based on it. 

Canola oil is characterized by a low level of saturated fatty acids (less than 4% palmitic acid) and relatively high levels of oleic acid (60%) and a-linolenic acid (10%). It is second only to olive oil, among the common fats and oils, in oleic acid level and, except for soybean oil, the only common dietary fat that contains a significant amount of a-linolenic acid. Furthermore, there is a favorable balance in the levels of linolenic and linoleic acids (viz., 18 3/18 2 ratio of 1 2) in canola oil. Canola oil has been found equally as effective as soybean oil, safflower oil, and sunflower oil in reducing plasma total and LDL cholesterol levels in normolipi-demic subjects. It also was effective in reducing plasma total and LDL cholesterol levels in hyperlipidemic subjects when it replaced saturated fat in their diets. Canola oil diets also have been shown to affect the fatty acid composition of blood... 

Detailed fatty acid composition of canola, soybean, sunflower, corn (maize), and flax oils as well as some specialty canola oils and HEAR oil are given in Table 2. 

TABLE 21. Fatty Acid Compositions and Soiid Fat indices of Lightiy Hydrogenated Canoia and Soybean Oii (Residuai C18 3 Content, 2 %). 

Fatty acid composition of regular flax oil is different from other commercial oils because of the very high contribution of ALA, usually above 50% (Table 2). Because of the high content of this unique fatty acid, flaxseed and flax oil are often used as food supplements, where enrichment with omega-3 fatty acids is needed. This fatty acid is susceptible to oxidation it oxidizes 20 0 times faster than oleic acid and 2 times faster than linoleic acid (8). This property makes the oil a good material for paint and plastic production where fast oxidation is required. Flax oil contains low amounts of saturated fatty acids (SFA) compared with low linolenic flax oil (Linola), soybean, and sunflower oils however, it is higher than canola oil (Table 2). Canola oil contains the lowest amount of SFA among all commercial oils. 

Cool temperatures during the 10-25 days after flowering are the main cause for higher amounts of linolenic acid in flax oils (14). For the same reason, flaxseed grown in the Canadian prairies, northern latimde, produce oils with higher levels of polyunsaturated fatty acids and lower contributions of oleic acid and samrated fatty acids. This phenomenon was also observed for other oilseeds such as sunflower, canola, and soybean (7, 13, 14). Similarly, a wide variation in fatty acid composition in Australian flaxseed samples was observed 13-25% of 18 1 and 46-64% of 18 3 (6). 

The fatty acid composition of the new crop has been modified, and the level of linolenic acid has been reduced from over 50% to 2% (6). This greatly improves oxidative stability of the oil, which by fatty acid composition is very close to sunflower and soybean oils (Table 2). Linola has been found to be more resistant to oxidation than regular flax oil, and its stability is comparable with soybean, canola, and sunflower oils (Przybylski, unpublished data). 

The fatty acid composition of soybean oil changes considerably with maturity and with seed oil deposition (15, 35, 43, 44). In typical soybean triacylglycerols, the palmitate and linolenate tend to decrease with maturity, whereas hnoleate increases. Oleate tends to increase to a maximum and then dechne slightly. Soybeans selected for atypical fatty acid compositions show quite different patterns of change with maturity from typical soybeans. 

Harp and Hammond (45) explored the stereospecific distribution of acyl groups on the three positions of the glycerol molecule for soybean triacylglycerols with a wide range in fatty acid composition. They found that the amount of an acyl group... 

Neff et al. (48, 49) partially separated the triacylglycerols of soybean oils with a wide range of fatty acid compositions using high-performance liquid... 

The physical properties of fatty acids vary with their chain length, unsaturation, and other substituents and change with temperature. Numerous attempts have been made to develop equations that will predict these properties. Soybean oil s properties should reflect its constituents and, especially, its fatty acid composition, and physical properties have frequently been measured for typical soybean oils, but there have been fewer measurements of soybean oils with modified fatty acid compositions. 

TABLE 8. The Onset, Maximum Rate, and Termination of Meiting Temperatures of Soybean Oii with Various Fatty Acid Compositions % (41). 

The estimated trans-acyl group intake by typical U.S. consumers is 11.1-27.6 g/ person/day (341). A comprehensive review concluded that trans-acyl groups consumed at 4.0% or more of total calories may raise plasma lipid levels (342). As a result of health concerns over the presence of trans-acyl groups in our diet, modifying fatty acid composition of soybean oil to improve its oxidative and flavor stability in ways similar to that obtained by hydrogenation, but without transformation, has become an objective of plant breeders. 

T. Wang, Phospholipid fatty acid composition of modihed soybeans and the effect of saturated fatty acid content on seed performance, Ph.D. Dissertation, Iowa State University, Ames, Iowa, 1998. 

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