Lipids wax esters

A group termed other esters includes a large variety of functionally diverse lipids. Wax esters are a typical example. The term wax is used commonly for esters of long-chain fatty acids with long-chain primary alcohols, but sometimes it is used for the entire mixture of lipids that contain waxes. Ester waxes are present in both plants and animals where they form the water-repellent surface coating (e.g., skin surface of animals and the leaf cuticle). Esters of normal alcohols with monobranched or multibranched fatty acids have been found in the preen glands of birds (2). Complex waxes (in which either the fatty acid or the alcohol component or both has a complex structure) have been isolated from some bacteria. Diesters... 

Generally, microalgae lipids include nentral lipids, polar lipids, wax esters, sterols, and hydrocarbons, as well as phenyl derivatives (Naik et al, 2010). For biodiesel prodnction, natural lipids, which are nonpolar, are always targeted. Typically, most of the lipids produced from microalgae strains that have been tested for biodiesel prodnction have fatty acid constitutions similar to most common vegetable oils (Becker, 2004 Huang et al., 2012), as shown in Table 6.1. 

Fig. 1. Structure of triacylglycerols (I), i.e. the typical reserve lipids of oil seeds, and of ionic and non-ionic polar lipids (II), such as glycerophospholipids and glycerogalactolipids, which function as membrane lipids. Wax esters (III) are only formed in jojoba (Simmondsia chinensis) seeds as energy reserves. (Rj, R2, R3 various acyl moieties R4 alkoxy moiety X various polar head groups of ionic and non-ionic membrane lipids)...

FIGURE 12.4 (A) Diagrammatic representation of the separation of major simple lipid classes on silica gel TLC — solvent system hexane diethylether formic acid (80 20 2) (CE = cholesteryl esters, WE = wax esters, HC = hydrocarbon, EEA = free fatty acids, TG = triacylglycerol, CHO = cholesterol, DG = diacylglycerol, PL = phospholipids and other complex lipids). (B) Diagrammatic representation of the separation of major phospholipids on silica gel TLC — solvent sytem chloroform methanol water (70 30 3) (PA = phosphatidic acid, PE = phosphatidylethanolamine, PS = phosphatidylserine, PC = phosphatidylcholine, SPM = sphingomyelin, LPC = Lysophosphatidylcholine). 

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]. 

Ethanol and choline glycerolipids were isolated from calf brain and beef heart lipids by PTLC using silica gel H plates. Pure ethanol amine and choline plasmalogens were obtained with a yield of 80% [74]. Four phosphohpid components in the purple membrane (Bacteriorhodopsin) of Halobacterium halobium were isolated and identified by PTLC. Separated phosphohpids were add-hydrolyzed and further analyzed by GC. Silica gel G pates were used to fractionate alkylglycerol according to the number of carbon atoms in the aliphatic moiety [24]. Sterol esters, wax esters, free sterols, and polar lipids in dogskin hpids were separated by PTLC. The fatty acid composition of each group was determined by GC. 

C2-C4 w-alkanes [42,43], and in supercritical carbon dioxide when employing novel surfactants with fluorocarbon tails [38,44], There is also interest in the further employment of lipids (triglycerides and wax esters, such as isopropyl myristate) as solvent to improve biocompatibility [45],... 

Determining the degree of hydrolysis of lipids is particularly interesting when degradation is being studied, since the hydrolysis of the ester bond is one of the main decay paths for triglycerides and wax esters. 

The potential for the preservation of lipids is relatively high since by definition they are hydrophobic and not susceptible to hydrolysis by water, unlike most amino acids and DNA. A wide range of fatty acids, sterols, acylglycerols, and wax esters have been identified in visible surface debris on pottery fragments or as residues absorbed into the permeable ceramic matrix. Isolation of lipids from these matrices is achieved by solvent extraction of powdered samples and analysis is often by the powerful and sensitive technique of combined gas chromatography-mass spectrometry (GC-MS see Section 8.4). This approach has been successfully used for the identification of ancient lipid residues, contributing to the study of artifact... 

Saponification (see Section 7.4) is carried out to extract more recalcitrant lipids, and the yields are higher than for conventional solvent extraction (Stern et al. 2000). 3 ml of 0.5 M methanolic NaOH is added to 0.1 g of the shard powder and heated at 70°C for 3 hours in a sealed glass vial. After cooling, the supernatant is acidified with HC1 and extracted with three aliquots of 3 ml //-hexane. The hexane will not mix with the methanolic solution (unlike the DCM MeOH used above), but will absorb the lipids and can be transferred into a new clean vial. The removal of excess hexane is carried out as above. Saponification will hydrolyze and methylate any ester functionalities, which removes the requirement to derivatize the samples (Section 7.4) unless other molecules are suspected of being present. However, any wax esters or triacylglycerols will also be hydrolyzed to their fatty acid methyl esters and alcohols therefore, if information on their composition is required, then conventional solvent extraction is recommended as a first step. For subsequent characterization of the lipid extract, see Chapter 7. 

Data from one escolar-associated outbreak found no correlation between BMI, age, health status, and amount of fish consumed to the severity and occurrence of symptoms, while other factors, such as variability in wax ester content in different fillet cut depths, could be relevant (Yohannes et al., 2002). Unlike some fish species, such as herring, which have uniform muscle oil content along the body (Brandes and Dietrich, 1953), muscle oil content in escolar and oilfish is not evenly distributed. Bone (1972) found that muscle oil content in oilfish increases from 14.5% (near vertebral column) to 24.7% (near the skin). A similar trend was also observed by Ruiz-Gutierrez et al. (1997) with higher oil content found in subcutaneous muscles than the periosteum. However, the lipid profile for... 

Fish with more than 10% wax esters in the total lipids of body tissues are uncommon. When higher levels of wax esters are found in epipelagic fish species, they are mainly stored in roe and the body lipids of these fish... 

Family0 Species name [valid name]fa Body part analyzed0 Wax esters (% of total lipid) References... 

The predominant lipid components in fish roes, like muscles, are triacylglycerols or phospholipids. Yet certain fish species have high levels of wax esters in their roes but not in muscles (Table 1.6) (Bledsoe et ah,... 

Hayashi, K. and Yamada, M. (1976). The lipids of marine animals from various habitat depths. V. Composition of wax esters and triglycerides of the gadoid fish, Podonema longipes. Bull. Faculty Fisheries Hokkaido Univ. 26,356-366. 

Mori, M., Yasuda, S., and Nishimuro, S. (1978). Two species of teleosts having wax esters or diacyl glyceryl ethers in the muscle as a major lipid. Bull. Jpn. Soc. Sci. Fisheries 44,... 

The composition of lipids from the silk and cuticule has been reviewed by Schulz (1997a, 1999). These lipids consist primarily of alkanes, as found in other arthropods, with 2-methylalkanes with an even number of carbon atoms in the chain being most abundant, with lesser amounts of alcohols, acids, aldehydes, and wax esters. Recently, a thorough analysis of the silk lipids of N. clavipes (Schulz, 2001) revealed a unique class of lipids from spider silk and cuticle, consisting of straight-chain and branched methyl ethers (1-methoxyalkanes, Fig. 4.4) with chain lengths between 25 and 45 carbon atoms. 

Lipids are esters of long-chain fatty acids and alcohols or of closely related derivatives. The chief difference between these substances is the type of alcohol in fixed oils and fats, glycerol combines with the fatty acids in waxes, the alcohol has a higher molecular weight, e.g., cetyl alcohols. 

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