Phytosterols in vegetable oils

Warner, K. and Mounts, T.L. 1990. Analysis of Tocopherols and Phytosterols in Vegetable Oils by HPLC with Evaporative Light-Scattering Detection. J. Am. Oil Chem. Soc. 67 827-831. 

Com germ oil contains two phytosterol lipid classes, free phytosterols and phytosterol fatty acyl esters (Table 10.1). Phytosterols have been recognized as one of the twelve most important classes of phytonutrients (Fahey et al. 1999). Most chemical identification of phytosterols in vegetable oils has been conducted by saponifying (hydrolyzing with base) the oil and measuring the resulting free phytosterols, usually by GLC (Table 10.4). The major phytosterols... 

K Warner, TL Mounts. Analysis of tocopherols and phytosterols in vegetable oils by HPLC with evaporative hght-scattering detection. J Am Oil Chem Soc 67 827-831, 1990. 

The composition of major sterols found in several vegetable oils is shown in Table 3.41. The total content of phytosterols in vegetable oils is given in Table 3.42. Usually, vegetable oils contain a mixture of phytosterols and related compounds, which are characteristic of a particular oh. Cholesterol is also a phytosterol as it is found in many vegetable oils, but is usually present at very low levels that have no practical importance in the nutritional balance. Vegetable oils also contain numerous 4,4-dimethylsterols and 4-methylsterols in small quantities. The contents of these compounds and other steroids in maize oil are given in Table 3.43 as an example. 

Assay Not less than 86.0% of Vegetable Oil Phytosterol Esters and not more than 9.0% of free vegetable oil sterols, the sum not less than 95.0%. Not less than 59.0% of des-methyl-sterols. Not more than 5.0% of acyl-glycerides. The vegetable oil sterols in Vegetable Oil Phytosterol Esters show the following typical distribution ... 

Canola oil contains a relatively high level of phytosterols (892 mg/100 g), about twice the level in soybean oil or sunflower oil (436 and 496 mg/100 g respectively) (Table 8). p-Sitosterol accounts for about 50%, campesterol 35%, and brassicasterol 14% of the total phytosterols in canola oil. Canola oil is the only common vegetable oil that contains brassicasterol. Plant sterols have been reported to lower plasma cholesterol level (107) by inhibiting the absorption of dietary cholesterol and the reabsorption of biliary cholesterol (108). 

Animal fats, such as milkfat, tallow, and fish oils, are characterized by the exclusive presence of cholesterol, whereas the sterol fraction in vegetable oils consist of a wide group of compounds also known as phytosterols. 

Plant sterols, also called phytosterols, have been reported to include over 250 different sterols and related compounds in various terrestrial and marine materials (Akihisa et al., 1991). Sitosterol, stigmasterol, and campesterol are the commonly consumed plant sterols. The predominant sterol class in vegetable oils is 4-desmethyl sterols. Sitosterol usually contributes more than 50% of desmethyl sterols. The other most significant desmethyl sterols include campesterol, stigmasterol, A5-avenasterol, A7-avenasterol, and A7-stigmastenol. Brassicasterol is a typical sterol for rapeseed and other Cruciferae. Stanol occurs in significant amounts in com bran and fiber oil (Piironen, et al., 2000). 

Other common food lipids are the sterols and to-copherols. Sterols are generally present in natural oils as both the free sterol and sterol fatty esters. Animal fats exhibit solely cholesterol while plant lipids contain a range of phytosterols. Tocopherols are found in vegetable oils as a mixture of four iso-mers a-tocopherol (true vitamin E) and 3-, y-, and d-tocopherol. Four unsaturated analogs, tocotrienols, exist with the same numbering terminology and are particularly abundant in palm oil. 

Phytosterols have cholesterol-lowering properties reducing cholesterol absorption in intestines, and may act in cancer prevention. Phytosterols naturally occur in small amount in vegetable oils, especially soybean oil. Sterols can reduce cholesterol in human subjects by up to 15% (Rossi S, 2006). 

Most of the unsaponifiables in vegetable and animal fats are sterols. The animal fats contain predominantly cholesterol, and most vegetable fats contain only traces of this sterol. Plant sterols, collectively called phytosterols, are made up mainly of sitosterols and stigmasterol, but some individual vegetable fats contain additional phytosterols. The pattern of typical sterols has been suggested as useful in detecting the adulteration of one oil with another (2). 

This approach can be extended to a large number of natural products rich in compounds with desirable biological activity, which include fruits and other plants -for example, the recovery of phytosterols and tocopherol from vegetable oils, as well as natural marine products. 

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... 

Commercial com oil has been recognized as having the highest levels of unsaponifiables (1.3-2.3%) of all commercial vegetable oils (6). The three most abundant chemical components in the unsaponifiable fraction of corn oil are phytosterols, tocopherols, and squalene. 

Sterols or phytosterols are present in flax oils at a level lower than those in many vegetable oils, 2.3 mg/g in flaxseed oil versus 4.1 to 6.9 mg/g in other oils (Table 2). The composition of sterols was similar to other oils, where p-sitosterol was the main component followed by campesterol and A -avenasterol. Brassicasterol was found in trace amounts in flax oil. This phytosterol is characteristic to plants from the Brassica family and often is used as a marker for oil adulteration (Table 2). 

Phytosterols are industrially isolated from the distillates, resulting from the deodorization of vegetable oils (1, 34—36). Phytosterols are sometimes hydrogenated to produce phytostanols (37). As the solubility of sterols and stanols is very low (< 1% at 25°C), it limits their application in food products. Esterification of sterol and stanols is, therefore, performed to make them fat-soluble and easy to incorporate in food products (37, 38). Two margarines containing 8-9% sterols (Becel Proactiv of Unilever) or stanols (Benecol of Raisio), in the form of esters, are now available in the markets in Europe and the United States. 

Phytosterols are found in most common vegetable oils. For example, soybean oil, one of the most commonly consumed oils, is reported to contain approximately 0.36% sterols and 0.124% tocopherols (15). The effect of phytosterols on the reduction of serum cholesterol has been attributed to the possible inhibition of intestinal reabsorption of circulating cholesterol. The saturated version of sterols, stanols, is reported to be more readily metbolized, and this has led to the development of nutritional supplements and it is used commercially in food products such as margarines. The main stanol reported for this application is sitostanol, a saturated derivative of sitosterol. Sterol and cholesterol are used by the human body to synthesize important hormones such testosterone and progesterone, which are used also in many pharmaceutical applications. 

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