Phytosterols structure

Winkler, J.K. and Warner, K. (2008) Effect of phytosterol structure on thermal polymerization of heated soybean oil. European Journal of Lipid Science and Technology, 110(11), 1068-1077. 

The order Caryophyllales is composed of 12 families (Fig. 1) and was selected for a chemosystematic analysis of sterols based on early reports of 24-alkyl-A7-sterols in three families i.e. Spinacia (Chenopodiaceae), Lophocereus (Cactaceae) and Phytolacca (Phytolaccaceae) . Phytosterol structure and composition was analyzed with respect to each plant s taxonomic assignment. Isolation, identification methods, taxonomic classification, nomenclature systems and tribal arrangements are presented elsewhere only mature photosynthetic tissue was analyzed to avoid... 

Tenerife and La Palma, revealed the existence of luteolin and an array of simple phenolic derivatives as well as three known phytosterols, B-amyrin, sitosterol, and stigmasterol. The phenols identified comprised a set of phenylpropanoids myristicin [566] (see Fig. 6.16 for structures 566-573), methyleugenol [567], todadiol [568], todatriol [569], crocatone [570], elemicin [571], apiole [572], and the coumarin scopoletin [573]. The occurrence of these compounds is recorded in Table 6.5. The differences between the two profiles were taken by Gonzalez and his co-workers... 

Phytosterols have been demonstrated as being anti-cancer components in the diet (Awad and Fink 2000). Scientific studies indicate that phytosterols may offer profection against colon, breast and prostate cancers (Vanderhaeghe and Bouic, 2000). The possible mechanisms, as reported by these authors, include the effect of phytosterols on membrane structure and function and on the signal transduction pathways that regulate tumor growth and apoptosis. The rice bran derived phytosterol-cycloartenol-ferulic acid ester on the central nervous system has been studied by Hiraga et al. (1993). 

Moreau RA, Whitaker BD and Hicks KB. 2002. Phytosterols, phytostanols, and their conjugates in foods structural diversity, quantitative analysis, and health-promoting uses. Prog Lipid Res 41 457-500. 

Cardiolipin or diphosphatidyl glycerol is one of the most ancient membrane phospholipids from phylogenic aspects. It is surprising for such a complex molecule as cardiolipin to have evolved as one of the major membrane lipids in prokaryotics, when steroids such as cholesterol and phytosterols did not. In eukaryotic cells, cardiolipin is exclusively localized within the mitochondria where it is particularly emiched in the outer leaflet of the inner membrane. Even though a molecular structure of cardiolipin has been conserved in entire organisms, its biological significance has escaped attention except in the case of anti-cardiolipin auto-antibodies which are clinically associated with the Wasserman reaction. 

For cholesterol absorption, one can take advantage of the fact that plant sterols (phytosterols) are poorly absorbed by mice and humans despite close structural similarity to cholesterol. Beta sitosterol, for example, differs from cholesterol only by the addition of an ethyl group to carbon 24 of the sterol side chain (see Fig. 10.1). This reduces absorption to 6% (34, 35) as compared to 60-80% for cholesterol. Sitostanol, which has a saturated C5-C6 bond in addition to the ethyl group, is only absorbed at 3% (34, 35) and is widely used as a non-absorbed sterol marker (Fig. 10.1). 

Fig. 10.1. Structures of cholesterol and a commonly used phytosterol. Adding a branch to the side chain and removing the double bond in the sterol B ring combine to reduce absorption of sitostanol —20-fold as compared to cholesterol.

Phytosterols are structurally very similar to cholesterol and the major phytosterols (campesterol, sitosterol and stigmasterol) have the same kind of membrane viscosity modulating function in plants that cholesterol (C27 3-OH-C6 C6 G61 C5—C8) has in animals. Campesterol (24-methylcholesterol), sitosterol (24-ethylcholesterol) and stigmasterol (A22, 24-ethylcholesterol) are widespread phytosterols. The animal sterols lanosterol and cholesterol are present in particular plants. Phytosterol esters reduce cholesterol absorption and lower LDL-cholesterol. 

The range of food components now considered as bioactives include vitamins, minerals, functional lipids, probiotics, amino acids, peptides and proteins, phytosterols, phytochemicals and antioxidants (Wildman 2001). Their structure and function vary widely and are important considerations when adding them to food. The health aspects of bioactive ingredients and functional foods are not covered here as they are beyond the scope of this chapter. 

Figure 10.1 Examples of structural formulas of phytosterol and sterol conjugates. FS = free sterol alcohol, SE = sterol fatty acid ester, SF = steryl ferulate, SG = steryl glycoside, ASG = acylated steryl glycoside.

The columns used for the GC separation of phytosterols are currently almost exclusively capillary columns with 0.1-0.3 mm internal diameter, and fused-silica capillary columns with chemically bonded stationary phases are commonly used (Abidi, 2001). The best separation of structurally very similar sterols, such as sitosterol and its saturated counterpart sitostanol, is obtained with slightly polar stationary phases like 5% diphenyl-95% dimethylpolysiloxane, and they are currently the most used columns for the separation of phytosterols (Lagarda et al., 2006). For detailed lists of different columns used in sterol analysis, see the papers by Abidi (2001) and Lagarda (2006). 

Phytosterols are partially absorbed in the small intestine. Human absorption efficiency is estimated to be approximately 10% for campesterol and campestanol, 4 to 5% for sitosterol and stigmasterol, and negligible for sitostanol. The absorption of cholesterol ranges from 33 to 60%. Structural features, including the length and configuration of the aliphatic side chain of phytosterols, are thought to contribute to the differences in the absorption efficiency between phytosterols and cholesterol. " Phytosterols apparently displace cholesterol by mass action and... 

Just as all animal tissues and foods contain cholesterol, which is needed for life itself, all plants have phytosterols, plant sterols. The molecular structures of cholesterol and phytosterols are virtually identical (see the illustration). Because they are so similar, the human body cannot tell the difference. 

Sound too good to be true More than twelve hundred research studies, conducted at top medical centers around the world and published in the most prestigious medical journals, document both the safety and efficacy of phytosterols in cholesterol control. They are completely safe not only because they are naturally found in plants but also because they never enter the bloodstream. After blocking the receptor micelles for probably one to two hours, they are rejected, owing to the slight difference in molecular structure, and are eliminated by the body. Even children and pregnant women can take them without fear. 

Recent developments in the area of oils and fats has led to the production of specialty lipids from novel sources such as fruit seeds, nuts, and other minor plant sources. In addition, preparation of structured lipids for a myriad of applications has been of interest. Minor components of oils and fats may be isolated during processing and used as nutraceutical and functional food ingredients. Examples are lecithin, phytosterols, tocopherols, and tocotrienols, among others. Obviously, the health-promoting potential of such products is also of interest. 

The chemical structure of phytosterols is similar to that of cholesterol so that these compounds may be involved in oxidative reactions. Przybylski and Eskin (42) found some oxidation products formed from plant sterols during storage of fried food products. Similar oxidation products were found in soybean oil and wheat flour (43). In light of health concerns associated with cholesterol oxidation products, potential health risks of phytosterol oxidation products are now receiving serious attention. 

Figure 1. Structures of the common sterols (phytosterols) In corn and their comparison with cholesterol, the main sterol In animals. Note that cholesterol has 27 carbons, campesterol has 28 carbons, and all of the other phytosterols shown have 29 carbons.

Phjdosterols and cholesterol have similar structures phytosterols are therefore competitors of cholesterol absorption. Consumption of phytosterol may lower blood cholesterol and thus protect from cardiovascular diseases (29). Phytosterol, especially, p-sitosterol, inhibits the growth of human colon cancer cell (30), prostate cancer cell (31), and breast cancer cell (32). 

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