Vegetable oils polyunsaturated fatty acids

Cooking oils contain esters of polyunsaturated fatty acids. You need not worry now about what esters are we will discuss them in Chapter 14. The important point here is that all vegetable oils contain fatty acids with long hydrocarbon chains, many of which have one or more carbon-carbon double bonds. (See Problem 4.44 for the structures of three of these fatty acids.) Autoxidation takes place at a carbon ac acent to a double bond— that is, at an allylic carbon. 

Prostaglandins arise from unsaturated C20 carboxylic acids such as arachidonic acid (see Table 26 1) Mammals cannot biosynthesize arachidonic acid directly They obtain Imoleic acid (Table 26 1) from vegetable oils m their diet and extend the car bon chain of Imoleic acid from 18 to 20 carbons while introducing two more double bonds Lmoleic acid is said to be an essential fatty acid, forming part of the dietary requirement of mammals Animals fed on diets that are deficient m Imoleic acid grow poorly and suffer a number of other disorders some of which are reversed on feed mg them vegetable oils rich m Imoleic acid and other polyunsaturated fatty acids One function of these substances is to provide the raw materials for prostaglandin biosynthesis... 

Com oil s flavor, color, stabiHty, retained clarity at refrigerator temperatures, polyunsaturated fatty acid composition, and vitamin E content make it a premium vegetable oil. The major uses are frying or salad appHcations (50%) and margarine formulations (35%). 

Polyunsaturated fatty acids in vegetable oils, particularly finolenic 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 minimum exposure to air, protection from light, and selective hydrogenation to decrease the finolenate content to ca 3% (74). Careful quality control is essential for the production of acceptable edible soybean oil products (75). 

Although vegetable oils usually contain a higher proportion of nnsatnrated fatty acids than do animal oils and fats, several plant oils are actually high in saturated fats. Palm oil is low in polyunsaturated fatty acids and particularly high in (saturated) palmitic acid (whence the name palmitic). Coconut oil is particularly high in lanric and myristic acids (both saturated) and contains very few nnsatnrated fatty acids. 

Conversion yields in the bienzymatic system have been optimized by using pure substrates (triglycerides) as well as crude vegetable oils (Table 4) rich in a range of polyunsaturated fatty acids (sunflower oil or linseed oil). The use of crude reactants approaches a more realistic scenario for the industrial-scale manufacture of hydropexides. 

E Group active derivatives of tocol and tocotrienol most active is RRR-a-tocoferol = (d)-a-tocoferol Vegetable oils and cereals, vegetables, fruit Depending on the amount of polyunsaturated fatty acids (PUFA) in the diet <1/2 yr 2.9 a-TE 1/2-1 yr 3.6 a-TE 1-19 yr 5.5 up to 13.3 a-TE >19 yr 13 down to 8.3 a-TE pregnancy 0.6 a-TE extra lactating women 2.7 a-TE extra... 

Lipids are highly digestible and provide both calories and essential fatty acids. Vegetable oils are generally high in polyunsaturated fatty acids, and therefore are high in... 

Vegetable oils are rich sources of vitamin E, whereas liver and eggs contain moderate amounts. The RDA for a-tocopherol is 10 mg for men and 8 mg for women. Vitamin E requirement increases as the intake of polyunsaturated fatty acid increases. 

Polymers Unsaturated fatty-acid chains offer opportunities for polymerisation that can be exploited to develop uses in surface coatings and plastics manufacturing. Polyunsaturated fatty acids can be dimerised to produce feedstocks for polyamide resin (nylon) production. Work is also ongoing to develop polyurethanes from vegetable oils through manipulation of functionality in the fatty-acid chains, to produce both rigid foams and elastomers with applications in seals, adhesives and moulded flexible parts (see Chapter 5 for more information). 

Plant oils are excellent sources of some valuable compounds such as unsaturated fatty acids, phytosterols, squalene, pigments, antioxidants, vitamins, waxes, glycolipids, and lipoproteins. Plant oils could be employed for technological uses as biodiesel, lubricants, surfactants, emulsifiers, biopolymers, and so on. Vegetable oils also can serve as appropriate sources for the production of valuable compounds having applications in food, pharmaceutical, medical, and environmental fields. Attention has been focused on various types of value-added fatty acids (polyunsaturated fatty acids, conjugated fatty... 

Canola Oil Canola oil is obtained from low erucic acid, low glucosinolate rapeseed. The unique polyunsaturated fatty acid and low saturated composition of canola oil differentiates it from other oils. It has a higher oleic acid (18 1) content (55%) and lower linoleic acid (18 2) content (26%) than most other vegetable oils, but it contains 8-12% of linolenic acid (18 3) (58). Canola oil is most widely used in Canada and is considered a nutritionally balanced oil because of its favorable ratio of near 2 1 for linoleic to linolenic acid content. Unlike most other edible oils, the major breakdown products of canola oil are the cis, trans- and tram, trans-2,4-heptadienals with an odor character generally described as oily, fatty, and putty. Stored canola oil shows a sharp increase in the content of its degradation products, which are well above their odor detection thresholds. The aroma is dominated by cis, tram-, tram, frani-2,4-heptadienals, hexanal, nonanal, and the cis, trans- and... 

Typical values for the specific gravity of canola oil are shown in Table 13. Ackman and Eaton (56) indicated that a different proportion between eicosenoic (C20 l) and octadecanoic, polyunsaturated fatty acids could be a major factor in changing the relative density of canola oil. Noureddini et al. (57) described relationship between temperature and density of vegetable oils including canola. As for other liquids, the density for vegetable oils is temperature dependent and decreases in value when the temperature increases. The same authors also modified the Rackett equation to calculate density, which is based on the composition of fatty acids. 

Monounsaturated fatty acids. The report that monounsaturated fatty acids (viz., oleic acid) were just as effective as polyunsaturated fatty acids (viz., linoleic acid) in lowering plasma total and low-density lipoprotein (LDL) cholesterol (100) aroused interest in the nutritional properties of canola oil. Canola oil contains 60% oleic acid and is second only to olive oil, among the common vegetable oils, in oleic acid content. Although avocado oil and high-oleic sunflower oil also contain high levels of oleic acid (>70%), they are minor constituents in the average diet. 

Standard canola oil is high in CIS fatty acids, about 95%, which is higher than the other commodity vegetable oils. It is high in CIS In - 9 oleic acid at about 60%, much higher than any other vegetable oils, and it is relatively low in polyunsaturated fatty acids, linoleic at about 21%, and linolenic at about 10%. Viscosity, cold hlter plugging point, and cetane number are some of the most important biodiesel fuel properties influenced by fatty acid composition. 

The amount of polyunsaturated fatty acids (PUFA) affects both melting and flashpoints of vegetable oils. Melting temperature of oil is directly related to the melting point of fatty acids, which decreases with unsaturation (7). The flash point of flaxseed oil is relatively low compared with other vegetable oils this can be attributed to a high contribution of PUFA. 

Oxidation. Oxidation of oils and fats is due to prolonged exposure to air. By virtue of the low polyunsaturated fatty acid content, palm oil is relatively more stable to oxidative deterioration than the polyunsaturated vegetable oils. However, in the presence of trace metals such as iron and copper, excessive oxidation at the olefin bonds of the oleic and linoleic acids can occur, resulting in rancidity. Highly oxidized crude palm oil is known to have poor bleachability and thus requires more bleaching earth and more severe refining conditions, and the final product will likely be of poor stability (44, 45, 68). 

Lubricants Mineral-based lubricants lead the lubricant market. However, with the advancement of the need for biodegradable products, vegetable oils have become popular, because of they are also better lubricants. The fatty acid composition of vegetable oils, however, is one major disadvantage. Oils rich in saturated fatty acids have poor low-temperature flow properties, and those rich in polyunsaturated fatty acids are of low oxidative resistance. Vegetable oils rich in monoun-samrated fatty acids have optimum oxidative stability and low-temperature properties (125). 

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