Linolenate content, of soybean

The fatty acid composition of soybean oil is influenced by growing conditions, especially temperature during oil deposition in the later stages of seed development. The linoleate and linolenate content of soybeans is increased by low temperature (Howell and Collins, 1957). The linolenate content of A5 particularly can be increased by low temperatures, and it is important to plant this variety early so that it matures under warm conditions (Hammond and Fehr, 1984 Rennie and Tanner, 1989). Although soybean mutants with elevated oleate levels are common, efforts to produce a line with consistently elevated oleate percentages have been frustrated by temperature effects. The line shown in Table 4.3 with an oleate concentration of 70% was produced under warm weather conditions. In a year where the growing season was cool it might drop to <50% oleate. 

IDENTIFICATION OF PROTEINS ASSOCIATED WITH CHANGES IN THE LINOLENATE CONTENT OF SOYBEAN COTYLEDONS... 

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. 

Genetic modification has shown to be an effective means to alter tocopherol contents of soybeans (Mounts et al, 1996 Almonor et al., 1998). The most abundant y-tocopherol is positively correlated with the most unsaturated linolenic acid content. Therefore, soybean lines with reduced linolenate currently developed to replace some hydrogenated oils containing rraws-fatty acids will have lower y-tocopherol contents. However, these lines tend to have higher a-tocopherol contents. 

McCord, K.L. W.R. Fehr T. Wang G.A. Welke S.R. Cianzio S.R. Schnebly. Tocopherol content of soybean lines with reduced linolenate in the seed oil. Crop Sci. 2004, 44, 772-776. 

The work of the plant breeder, however, is extremely slow and there is always the possibility that breeding in desired characteristics or breeding out undesired characteristics is accompanied by the elimination of other desirable features such as cold-or disease-resistance or high yield. Attempts to breed out the high linolenic acid content of soybean oil to improve flavour and oxidative stability have been disappointing. 

Howell, R.W. and Collins, F.I. (1957) Factors affecting linolenic and linoleic acid content of soybean oil. Agron. J. 49, 593-597. 

B. St John, and G. B. Collins, Reduction of linolenate content in soybean cotyledons by a substituted pyridazlnone. Phytochemistry (in reyiew). 

Whole soybeans contain 360-370 g/kg CP, whereas soybean meal contains 410-500 g/kg CP depending on efficiency of the oil-extraction process and the amount of residual hulls present. The oil has a high content of the polyunsaturated fatty acids, linoleic (08 2) and linolenic (08 3) acids. It also contains high amounts of another unsaturated fatty acid, oleic (08 1) and moderate amounts of the saturated fatty acids, palmitic (06 0) and stearic (08 0). 

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... 

Polyunsaturated fatty acids in vegetable oils, particulady linolenic esters in soybean oil, are especially sensitive to oxidation. Even a slight degree of oxidation, commonly referred to as flavor reversion, results in undesirable flavors, eg, beany, grassy, painty, or fishy. Oxidation is controlled by the exclusion of metal contaminants, eg, iron and copper addition of metal inactivators such as citric acid TniniTniiTn exposure to air, protection from light, and selective hydrogenation to decrease the linolenate content to ca 3% (74). Careful quality control is essential for the production of acceptable edible soybean oil products (75). 

For mminant fat to become directly responsive to dietary unsaturated fats, it is necessary to protect the lipids against saturation by rumen microorganisms. The alteration of the lipid content of mutton by the feeding of such protected oil supplements has been described (14). Also, it has been shown that a diet of extruded soybeans increased the linoleic acid and linolenic acid contents of steer adipose tissue (15). 

In neutral oils and fats, the fatty acids are not usually randomly distributed among different positions on the glycerol backbone and are associated in particular patterns. As an example, saturated fatty acids such as palmitic and stearic acids are associated with the sn- and sn-3 positions of soybean oil, albeit at higher proportions in the sn- position. However, the reverse is observed at high content of saturated fatty acids. Linoleic acid is preferably in the sn-2 position, whereas oleic acid is randomly distributed among the three positions. Linolenic acid is primarily at sn-2 followed by sn- and sn-3 positions. The stereospecific distribution of fatty acids has a marked effect on the oxidative stability of the resultant oils, and their presence at the sn-2 position helps their stability (19). 

The low total polyunsaturation of canola oil, about 30% versus 58% for soybean oil, along with the high content of monounsaturates, about 60% versus about 25% for soybean oil, are responsible for the good flavour stability of this oil, despite the presence of linolenic acid. Additional minor, but important reasons, for better oxidative stability of canola oil compared with soybean oil are as follows ... 

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. 

According to the composition indicated by the Codex Alimentarius (Codex-Stan 210-1999), the saturated fatty acid content of regular sunflower oil is lower than that in corn (maximum 22%), cottonseed (maximum 32%), peanut (maximum 28%), and soybean (maximum 20%) oils, and higher than the saturated content of safflower (maximum 12%) and rapeseed (maximum 12%) oils. The linolenic acid content (18 3) of regular sunflower oil is fairly low (always lower than 0.3%), giving the oil a good oxidative stability. 

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