Low-linolenate soybean oil

Because of worldwide interest in the health concerns of consuming trans fats, and subsequent food-labeling requirements for trans-iax content in the United Stastes and elsewhere, great interest in low-linolenate soybean oil (less than 3% linolenate) has arisen (Chapters Lipids, Food Uses for Soybean Oil and Alternatives to Trans Fatty Acids... 

From Gupta (2003). Standard shortening is made by partial hydrogenation interesterified shortening is a blend of 45% fully hydrogenated cottonseed oil and 55%% low-linolenic soybean oil. 

Abbreviations HEAR—High erucic rapeseed oil CAN—Canola oil LLCAN—Low linolenic canola oil HOCAN—High oleic canola oil HOLLCAN—High oleic low linolenic canola oil SOY—Soybean oil SUN—Sunflower oil. 

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. 

Protein, oil, and fiber percentages for oil from high-oleic, low-saturated fat, low-linolenic, lipoxygenase-free, high-cysteine soybeans, and commodity soybeans were determined by Wang and Johnson (2001). Table 6.7 shows that low-linolenic soybeans have much higher oil content (20.2 %) than other soybean types. Fiber percentages were lower for low-saturated fatty acid soybeans than for the other soybean types. 

Commercially available soybean oils have a triglyceride structure. Oleic (C18 l), linoleic (C18 2) and linolenic acid (C18 3) are the primary fatty acid components of soybean oils (Table I). Regular soybean oil (SOY) has approximately 4.5 C=C bonds per triglyceride, while low saturation soybean oil (LSS) has approximately 5.1 C=C bonds. LSS oil is a commercially available soybean oil with considerably more linoleic acid 4). The fatty acid side chains in these two soybean oils are non- conjugated. Conjugated LSS oil (CLS) has been prepared in our laboratories from LSS by Rh-catalyzed isomerization 36). 

Pd(acac)2 has been reported to be an active catalyst in soybean oil hydrogenation [47]. The reactions were conducted in bulk with low catalyst loadings (1-60 ppm) and without any co-catalyst. Under 10 atm H2 pressure and at 80-120 °C, optimum linolenate selectivity and high trans-isomers content were obtained. Decomposition of the catalyst occurred at temperatures above 120 °C. 

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... 

Soybean oil and other fats and oils containing linolenic acid show the reversion phenomenon when exposed to air. Reversion flavor is a particular type of oxidized flavor that develops at comparatively low levels of oxidation. The off-flavors may develop in oils... 

The development of a characteristic, objectionable, beany, grassy, and hay-like flavor in soybean oil, commonly known as reversion flavor, is a classic problem of the food industry. Soybean oil tends to develop this objectionable flavor when its peroxide value is still as low as a few meq/kg, whereas other vegetable oils, such as cottonseed, com, and sunflower, do not (15, 51). Smouse and Chang (52) identified 71 compounds in the volatiles of a typical reverted-but-not-rancid soybean oil. They reported that 2-pentylfuran formed from the autoxidation of linoleic acid, which is the major fatty acid of soybean oil, and contributes significantly to the beany and grassy flavor of soybean oil. Other compounds identified in the reverted soybean oil also have fatty acids as their precursors. For example, the green bean flavor is caused by c/i-3-hexenal, which is formed by the autoxidation of linolenic acid that usually constitutes 2-11% in soybean oil. Linoleic acid oxidized to l-octen-3-ol, which is characterized by its mushroom-like flavor (53). 

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... 

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 ... 

Predominate use of a particular oil in a given region of the world is dependant on world trade movement. For many years, cottonseed oil was the main source of cooking and salad oils in the United States. However, since World War II, soybean oil has become the most prominent oil. Other oils, particularly those with high oleic content or low linolenic content, are becoming more important, as they do not require hydrogenation for stability (14, 15). Typical compositions of some commercially important cooking and salad oils are shown in Table 1. 

Figure 2.3 Oxidation and tocopherol retention during modified (A) and conventional (B) refining of various types of soybean oils. Key —0—, high-oleic acid soybean oil (HO) — —, low-linolenic acid soybean oil (LLL) —A—, lipoxygenase-free soybean oil (LOX) —K—, low-saturated fatty acid soybean oil (LS) — —, commodity soybean oil (CS). Source Wang and Johnson 2001b.

The high degree of unsaturation, particularly the significant level of linolenic acid, of soybean oil limits its food application due to its low oxidative stability. Partial hydrogenation is used to increase the melting temperature and, at the same time, to improve the oxidative stability of soybean oil. 

Sensory evaluation provides information most closely associated with the quality of food lipids. Flavor or odor defects may be detected by panelists before they are recognised by chemical or instrumental methods. For example, the fishy and grassy taste produced in linolenic acid-containing oils such as soybean oil occurs at very low levels of oxidation only detected by sensory analyses. The limitations of this method are poor reproducibility and high cost of panelists and the necessary facilities. The recommended approach is to use more reproducible chemical or instrumental methods to complement or support the sensory analyses (Frankel 1998). 

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