Fatty acid steryl esters

Major compound classes Resin acids, mono terpeno ids, other terpenoids Fats, fatty acids, steryl esters, sterols Phenolic substances sugars, starch, proteins Inorganics... 

Sterols are substituted with an isoprenoid side chain at C-17 (Fig. 120). In plants they may be glycosylated (steryl glycosides) or acylated by fatty acids (steryl esters) at the C-3 hydroxy group. Acylated steryl glycosides, e.g., 6-0-palmitoyl-/8-D-glucosyl-sitosterol, also occur in plants. Sterols are grouped according to the pattern of methylation into 4,4-dimethylsterols, e.g., lanosterol and cycloartenol, 4a-methylsterols, e.g., obtusifoliol, and 4-demethylsterols, e.g., cholesterol. 

Esterified by a fatty acid (steryl esters), e.g., sitosteryl palmitate (Sticher 2007 and references therein)... 

Extractives are compounds with low molecular weight which include, amongst others, lipids, phenolic compounds, terpenoids, fatty acids, resin acids, steryl esters, sterol. 

The analysis of plant steryl esters has typically proceeded by isolation of the steryl ester fraction from a plant lipid extract followed by saponification to yield the sterol and fatty acid moieties. These are then identified and quantified by GC analysis, usually after preparation of the fatty acid methyl esters. However, this method of analysis has the disadvantage that the integrities of the steryl esters are lost. With the often multicomponent mixtures of sterols and fatty acid methyl esters resulting from a typical plant steryl ester mixture... 

Although not very commonly used in the separation of nentral hpids, two-dimensional systems have been nsed to separate hydrocarbons, steryl esters, methyl esters, and mixed glycerides that move close to each other in one-dimensional systems. Complex neutral lipids of Biomphalaria glabrata have been first developed in hexane diethyl ether (80 20), dried, and the plates have been turned 90°, followed by the second development in hexane diethyl ether methanol (70 20 10) for complete separation of sterol and wax esters, triglycerides, free fatty acids, sterols, and monoglycerides [54]. 

Three pro-inflammatory steryl esters of furan fatty acids (11-13) have recently been isolated from the Mediterranean sponge Dictyonella incisa [30]. The furan moiety was clearly established by H and 13C NMR signals corresponding to... 

Sterols are minor constituents of most fats. Those of animal origin contain cholesterol and traces of other sterols, whereas plants contain phytosterols, of which p-sitosterol is the most common. Sterols occur in the free form or, after esterification to fatty acids through the 3-OH group, as steryl esters. The presence of sterols in archaeological residues can be a useful indicator of a plant or animal origin or an indicator of both if cholesterol and phytosterols are detected in the same sample. That noted, cholesterol is a potential contaminant of all archaeological samples subjected to handling. 

Saturated hydrocarbons Unsaturated hydrocarbons Wax esters Steryl esters Long chain aldehydes Triacylglycerols Long chain alcohols Free fatty acids Quinones Sterols... 

This enzyme [EC 3.1.1.13] (also known as cholesterol esterase, sterol esterase, cholesterol ester synthase, and triterpenol esterase) catalyzes the hydrolysis of a steryl ester to produce a sterol and a fatty acid anion. This class represents a group of enzymes exhibiting broad specificity. They act on esters of sterols and long-chain fatty acids, and may also bring about the esterification of sterols. These enzymes are typically activated by bile salts. See also Esterases D. P. Hajjar (1994) Adv. Enzymol. 69, 45. 

Figure D1.6.6 latroscan TLC-FID chromatograms of (A) a lipid fraction enriched with neutral lipids isolated from cod flesh and stored in ice (B) neutral lipids spiked with authentic 1 -0-palmityl-glyceryl ether dipalmitate (GE), coinciding in position with authentic highly unsaturated acids such as 22 6n-3 (C) hydrogenated neutral lipids spiked with GE. The solvent system was 97 3 1 (v/v/v) hexane/diethyl ether/formic acid for 40 min. Abbreviations O, origin SF, solvent front FFA, free fatty acid PL, phospholipids SE, steryl ester ST, free sterol TG, triglyceride. Reproduced from Ohshima et al. (1987) with permission from AOCS Press.

The sample is now ready for analysis using the procedures described above (see Basic-Protocol and Alternate Protocol). Figure D1.6.6 shows chromatograms of cod muscle lipids before and after hydrogenation. Note the single peaks for steryl esters and free fatty acids in panel C compared to the double peaks in panels A and B. 

Ferrari, R., Esteves, W. and Mukherjee, K. (1997) Alteration of steryl ester content and positional distribution of fatty acids in triacylglycerols by chemical and enzymatic interesterification of plant oils. J. Am. Oil Chem. Soc., 74(2), 93—96. 

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 preparation of high-purity tocopherols and phytosterols involves steps such as molecular distillation, adduct formation, liquid-liquid extraction, supercritical fluid extraction, saponification, and chromatography (175). The extraction of tocopherols from soybean oil deodorizer distillate by urea inclusion and saponification of free fatty acids resulted in good recovery of tocopherols (208). To improve the separation of sterols and tocopherols, Shimada et al. (209) used a lipase to esterify sterols with free fatty acids. Then the steryl esters and tocopherols were separated better by molecular distillation. Chang et al. (210) used supercritical fluid CO2 extraction to recover tocopherols and sterols from soybean oil deodorizer distillate. A patent by Sumner et al. (211) advocated treatment of the distillate with methanol to converted free fatty acids and other fatty acid esters to methyl esters that can then be removed by a stripping operation. Then separation of sterols and tocopherols could be carried out by molecular distillation. 

Free sterols are slightly less volatile than tocopherols (Figure 2). Deodorization of soybean oil under varying process conditions (temperature 220-260°C, low pressure 1.5 mbar and 1.5% steam) resulted in a 10-35% reduction of the total sterol content (20). This sterol reduction is totally attributed to the free sterol fraction because esterified sterols are not volatile under the conditions prevailing inside the deodorizer. In case of steam refining, an increase of the steryl ester content can sometimes be observed, probably because of a heat-promoted esterification reaction between free sterols and fatty acids (20). This phenomenon will not take place during deodorization of chemically neutralized oil because the initial FFA concentration is much lower in that case. 

A particular type of wax ester, a steryl ester, is produced where the alcohol unit to which the fatty acid is joined is a sterol.These are also waxy solids, an example being lanosteryl palmitate in lanolin, which is found on sheep s wool. 

High-molecular-weight esters, such as wax esters, steryl esters, triterpenoid esters and triacylglycerols, are often hydrolysed, after which the liberated moieties are GC analysed however, this procedure provides only limited compositional information. The very convenient one-pot small-scale hydrolysis-silylation procedure, applicable to ester-emulsifiers, oils, fats, wax esters and other hydrolysable lipids, has been proposed by the lUPAC (Briischweiler and Hautfeune, 1990). The procedure involves the saponification of esters (ca. 10 mg) in 0.5 N ethanolic KOH solution (0.25 mL) at 80 °C for 3 h, evaporation to dryness in a stream of nitrogen and then silylation of the hydrolysis products. This enables the components of very small samples to be determined (< 0.1 mg). This procedure was used for the hydrolysis of wax esters and triterpenoid esters in potato and eggplant cuticular waxes (Szafranek Synak, 2006 Halinski et al., 2009). A solution of 1-2% (v/v) concentrated sulphuric acid in methanol can be easily used for the transesterification of acyl lipids and the esterification of free fatty acids (Christie, 1994). More procedures for ester hydrolysis and transesterification and for fatty acid esterification are described in detail by Christie (1994). 

The field of fatty acid separation was revolutionized by the development of GC, which allowed nearly complete separation of the common fatty acids. Later workers developed methods for GC separation of steroids, and of the steryl and glyceryl esters by high-temperature GC. The introduction of the flame ionization detector (FID) transformed GC from a method of qualitative separation into a method of quantification, which has remained unsurpassed to the present day. In parallel, TLC was developed as both a preparative and analytical technique for the resolution of the nonvolatile lipids. Because of the nearly universal applicability to all lipid analyses and the use of inexpensive apparatus, TLC made lipid separations accessible to all laboratories and it has remained unsurpassed as a method of sample preparation for modern analytical methods of lipid analyses. 

Lanolin steryl ester determinations Lanolin is the wool grease secreted by the sheep sebaceous glands, and represents a complex mixture of high molecular mass lipids, including fatty acids and alcohols, sterols, hydroxyacids, diols, and aliphatic and steryl esters. Lanolin is widely used in cosmetic and pharmaceutical formulations. The study of minor lipids... 

Silver ion TLC has also been used for separation of a variety of substituted unsaturated fatty acids such as epoxy, hydroxy and halohydroxy fatty acids, and these have been reviewed by Morris and Nichols (1972). Wax esters and steryl esters exhibit similar polarities and do not separate on column chromatography or normal silica TLC. Kiosseoglou and Boskou (1990) have separated the wax esters from steryl esters by using argentation TLC. They have used silica gel plates impregnated with 10% silver nitrate, with developing solvent hexane/chloroform (7 3 vol./vol.). 

Kiosseoglou, V. and Boskou, D. (1990) Separation and fatty acid composition of steryl and wax esters in hexane extracts of sunflower seed, soybeans and tomato seeds. Lebensmittel-Wissenschaft and Technologie, 23 (4), 340-2. 

In Chapter 15, the biosynthesis of phytosterols was described. Briefly some of the major sterols found in plants are shown in Fig. 1. Principal differences are in the side chain (C20-CJ7) which has different degrees of substitution and unsaturation. The sterol derivatives, also shown in Fig. 1, are (1) steryl esters (SEs), in which a long-chain fatty acid is esterified at the 3-OH of the sterol, (2) steryl glycosides (SGs) in which the 3-OH of the sterol forms a glycosidic linkage to the 1-position of a monosaccharide, usually glu-... 

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