Triacylglycerol, definition

Two brief, but very definitive, reviews on the HPLC of triacylglycerols (Planner, 1981) and of phospholipids (Porter and Weenan, 1981) are recommended reading. 

Another promising area for adaptation of enzyme bioreactor technology is that of lipid modification. Several examples are a) the interesterification of triacylglycerols to change their composition b) limited lipolysis for production of flavors and c) conversion of cholesterol to forms that are not absorbed. The potential stabilization of enzymes to the presence of organic solvents would provide a definite advantage to enzyme bioreactor technology for the modification of lipid molecules. 

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. 

Lipids are naturally occurring organic molecules that have limited solub.ility in water and can be isolated from organi.sms by extraction with nonpolar organic solvents. 1-atS oils, waxes, many vitamins and hormones, and most nonprotein cell-membrane components are examples. Note that this definition differs from the sort used for carbohydrates and proteins in that lipids are defined by a physical property (solubility) rather than by structure. Of the many kinds of lipids, we ll be concerned in this chapter only with a few triacylglycerols, eicosanoids, terpenoids, and steroids. 

Lipids are insoluble in water and this profoundly affects the particular phenomena associated with their digestion, absorption, transport in the blood, and metabolism at the cellular level. Fat is easily recognized when it accumulates within the body, but the chemical and technical definition of fats and hpids are more difficult. Of nutritional interest are triacylglycerols (TAG), phospholipids (PL), sterols, and some derived lipids — results of the hydrolysis or enzymatic breakdown of simple and compound lipids. 

The proposed EEC definition of a CBE (cocoa butter equivalent) fat includes a limit on the percentage of SOS-type triacylglycerols in the fat. To determine the percentage of SOS, a lipolysis method as described in Section 6.2.17 followed by 1,3-random, 2-random calculation would be unsuitable except for whole natural fats. 

The breakdown of triacylglycerol is catalysed by lipases. A large number of such enzymes have been purified from animals, plants and microbes (cf. Brockerhoff and Jensen, 1974). It should be noted that the term lipase is frequently misused. A true lipase is one which attacks triacylglycerols and acts only at an oil-water interface. This definition therefore excludes enzymes acting on water-soluble esters (esterases) or those preferentially hydrolysing other lipids (acyl hydrolases). 

The chapter has examined advantages of TLC, definitions, structure, occurrence, function, sample preparation, sorbents, mobile phases, usual modes of development, and detection procedures for lipids. Although a discussion of 2-D lipid analysis has been provided, mention was not made of the newer technique of multiphase TLC, in which components are separated in two different directions according to different parameters, e.g., conventional silica gel in one direction and reversed phase in the other direction. Ritchie and Jee (143) have used this technique for the analysis of triacylglycerols. 

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