Waxes and Triacylglycerols

Waxes are found in many plants and animals. Natural waxes are found mi the surface of fiuits, and on the leaves and stems of plants where they help prevent loss of watM and damage from pests. Waxes on the skin, fur, and feathers of animals provide a waterproof coaling. A wax is an ester of a saturated fatty acid and a long-chain alcohoL each containing finom 14 to 30 carbon atrans. 

The formulas of some common waxes are given in Table 15.2. Beeswax obtained from honeycombs and camauba wax from palm trees are used to give a protective coating to furniture, cars, and floors. Jojoba wax is used in making candles and cosmetics such as lipstick. Lanolin, a mixture of waxes obtained from wool, is used in hand and facial lotions to aid retention of water, softening the skin. 

Type Condensed Structural Formula Source Uses 

Jojoba wax CH3 — (CH2) 18—C—0—(CH2) 19 — CHj Jojoba bush Candles, soaps, cosmetics 

In the body, fatty acids are stored as triacylglycerols, also called triglycerides, which are triesters of glycerol (a trihydroxy alcohol) and fatty acids. The general formula of a triacylglycerol follows  

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In the sediment from industrial winterization, additional minor fatty acids and alcohols with 26 to 32 carbon atoms in the chain have been found in waxes and triacylglycerols (15). Most of these compounds are extracted from the seed coat and can initiate sediment formation in canola oil (16). 

Waxes and Triacylglycerols Chemical Properties of Triacylglycerols Phospholipids Steroids Cholesterol, Bile Salts, and Steroid Hormones Cell Membranes... 

Analytical methods for determining the authenticity of vegetable fats have classically been based on comparison of the composition of some major and minor components. For the most important traded oils, tables of the composition (i.e. profiles) of the major fatty acids and sterols have been of importance and have in some cases been supported by data describing other components such as triacylglycerols, sterol esters, volatiles, waxes and fatty alcohols. 

Paraffin followed by candelilla wax and microcrystalline waxes, and eventually by beeswax, are considered as the most effective moisture barriers derived from edible waxes (Morillon et al. 2002). There is no satisfactory chemical definition for the term wax which is used for a variety of products of mineral, botanical and animal origin that contain various kinds of fatty materials (Table 23.4). The term resins or lacs can also be used for plant or insect secretions that take place along resins ducts, often in response to injury or infection, and result in more acidic substances (Hernandez 1994). However, all waxes tend to contain wax esters as major components, that is, esters of long-chain fatty alcohols with long chain fatty acids. Depending on their source, they may additionally include hydrocarbons, sterol esters, aliphatic aldehydes, primary and secondary alcohols, diols, ketones, triacylglycerols, and so on. 

Dewaxing Winterization is achieved by cooling an oil with the consequent crystallization of high melting point fractions (waxes and/or triacylglycerols). 

Species Tissues Hydrocarbons Wax and Sterol Ester Triacylglycerol Wax Alcohol and Sterol Monoacylglycerol Phosphatide Free Fatty Acid... 

Olive oil is often illegally adulterated with other less expensive vegetable oils. Oils widely used for this purpose include olive pomace oil, corn oil, peanut oil, cottonseed oil, sunflower oil, soybean oil, and poppy seed oil. °° Among the varions chemical and physical methods employed toward the detection of the adulteration of olive oil by low-grade olive oils and seed oils are (a) Sterol analysis (presence of stigmasterol and 3-sitosterol), (b) alkane analysis (C27, C29, and C31), (c) wax and aliphatic alcohol analysis, (d) fatty acids/(with HPLC) trans fatty acid, and (e) Triacylglycerol. 

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). 

Some examples of mammalian surface lipid composition can be seen in Table 3.196. It will be seen clearly that few generalizations can be made. Thus, the contents of sterols, sterol esters and wax esters are extremely variable while squalene, non-esterified fatty acids and triacylglycerols which are major components of human surface lipids are minor or absent from other animals. For further details of human surface lipids see Section 12.4 and for different animals refer to Downing (1976). 

The composition of skin surface lipids varies over the body but in sebaceous-enriched parts such as the face, scalp and upper trunk about 95% of the lipid is sebum (Greene et al, 1970). The epidermal portion contains mainly cholesterol, cholesterol esters and triacylglycerols. When sebum is freshly formed it consists mainly of triacylglycerols, wax esters and squalene (Table 12.4). Little or no unesterified fatty acid is present at first but this is generated by bacterial lipases. There are large differences in the skin surface... 

C24H48O2 M 368.642 Occurs in some waxes and less commonly in some triacylglycerols. Cryst. (AcOH). Mp 87.5-88 . Polymorphous. 

Wakeham, S. G. and Frew, N. M. (1982) Gas capillary gas chromatography-mass spectrometry of wax esters, steryl esters and triacylglycerols. Lipids, 17, 831-43. 

Lipids are present as ingredients in most foods and play key nutritional roles, being crucial for many physiological functions, they also can be used as food quality markers. For these reasons, the characterization of the lipid fraction present in fats and oils is important for the food industry. Following a general lipid classification, triacylglycerols (mono- and diderivatives), phospholipids, glycolipids, waxes, and sterol esters are included in the saponifiable fraction, whereas the nonsaponifiable... 

In some species, waxes serve the function of high-energy storage forms. Waxes are common in the oils of fish and other marine animals. The major lipids of commercial whale oil consist of approximately 65 percent waxes and 35 percent triacylglycerols. Essentially all of the oil in jojoba Simmondsia chiensis) seed is in wax form. Whale and jojoba oils have been valued for stability in heavy-duty lubrication applications, and jojoba oil has been used in a variety of cosmetics. 

Draw the condensed structural formula for a wax or triacylglycerol produced by the reaction of a fatty acid and an alcohol or glycerol. 

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). 

Waxes are biosynthesized by plants (e.g., leaf cuticular coatings) and insects (e.g., beeswax). Their chemical constituents vary with plant or animal type, but are mainly esters made from long-chain alcohols (C22-C34) and fatty acids with even carbon numbers dominant (Fig. 7.11). They may also contain alkanes, secondary alcohols, and ketones. The majority of wax components are fully saturated. The ester in waxes is more resistant to hydrolysis than the ester in triacylglycerols, which makes waxes less vulnerable to degradation, and therefore more likely to survive archaeologically. 

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