Chemical Properties of Triacylglycerols

Percent (m/m) saturated and unsaturated fatty acids in selected fats and oils I Polyunsaturated B Monounsaturated B Saturated 

FIGURE 15.4 Vegetable oils are liquids at room temperature because they have a higher percentage of unsaturated fatty acids than do animal fats. 

LEARNING GOAL Draw the condensed structural formula 

19 Draw the condensed structural formula for the ester in beeswax that is formed from myricyl alcohol, CH3— (012)29—OH and palmitic acid. 

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

The physical and chemical properties of individual oils and fats are determined by the nature and proportions of fatty acids that enter into the triglycerides composition. Animal and dairy fat like plant oils are dominated by triacylglycerols, with steroids present as minor components, cholesterol and its esters being the most significant. The triacylglycerols of animal fats differ from plant oils since they contain more of the saturated fatty acids and consequently are solid at room temperature. 

The number of double bonds in a fatty ester radical significantly affects both physical and chemical properties of the triacylglycerol. The highly unsaturated (three double bonds) linolenic acid (18 3) is unstable to oxidation, and undesirable odors and flavors can develop. The rate of oxidation 18 3 is 15-fold greater than that of oleic acid (18 1). 

Triacylglycerols are quantitatively the most important class of dietary fats. Their biologic properties are determined by the chemical nature of the constituent fatty acids, in particular, the presence or absence of double bonds, the number and location of the double bonds, and the cis-trans configuration of the unsaturated fatty acids. 

Interesterification involves an exchange of acyl groups within and between triacylglycerol molecules. This re-distribution of the fatty acids results in modification of the physical properties and nutritional properties of the fat (Frede, 1991). The traditional process of interesterification involves the use of chemicals. 

There is considerable interest in the chemical composition and properties of citrus oils and essences as well as the role they play in food and nonfood industries. Citrus peel oils and essences possess a pleasant aroma, with oxygenated compounds being the major constituents that account for their characteristic odor. Terpenes, the most abundant components in cold-pressed citms peel oil, are removed in concentrated oil production, usually by use of adsorbant and supercritical carbon dioxide, to increase the concentration of oxygenated compounds and to enhance the qualification of the oil. Meanwhile, citms seed oils are composed largely of triacylglycerols and are rich in oleic and linoleic acids. 

Initially, non-polar stationary phases only (of the methyl silicone type) were used in high-temperature GC, and cross-linking and chemical-bonding improved the properties of the columns appreciably. More polar bonded phases, consisting of phenylmethyl silicones, later came into use and are available commercially. At present, these have a temperature limit of about 360 C, and while this will no doubt be improved, the ultimate limit may depend on the pyrolysis temperature of triacylglycerols. The optimum thickness of the liquid film for high-temperature GC is about 0.1 to 0.12 o.m. 

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