Trans Fatty acids physical properties

Trans fatty acids have higher melting points than their cis counterparts, while saturated fatty acids have higher melting points than both trans and cis fatty acids. For example, the melting points of Cig fatty acids are 69.6°C for stearic acid (18 0), 44.8 °C for elaidic acid (trans-lS l), and 13.2 °C for oleic acid (cis-18 1). The relative proportion of these different types of fatty acids influences the physical properties of cooking fats and their suitability for different uses in the food processing industry. 

These trans compounds have different physical properties than natural cis isomers and are readily separated with gas chromatography analysis. The detection of trans isomer fatty acids in an olive oil indicates addition of seed oils to olive oil, of refined olive oil to virgin olive oil and of esterified oil to residue olive oil and olive oil. 

The physical properties, such as melting points, specific heat, viscosity, density, and refractive index depend on the type of fatty acids present in the triglyceride and their location, chain length of fatty acids, number and location of cis and trans double bonds on the fatty acid chains as well as compatibility of the different triglycerides in the mixture and the type of crystal present. 

Cis double bonds produce a kink, or a bend, of about 30 degrees for each double bond into the backbone, and these can flip over to the trans form under high temperatures. Trans double bonds allow the molecule to lie in a straight line however, the human body cannot convert the trans form into nutrients and so prevents the metabolic activities from converting it to the active cis forms. This can lead to a deficiency in essential fatty acids. The more double bonds, and therefore more kinks, the more beneficial it is to human health. By completely changing the physical and chemical properties, the kinks allow essential protein associations to form more easily, thus permitting more saturated fatty acids to disperse and interact with water or blood. 

Food and feed quality begins with the selection of the best-quality ingredients, which are evaluated in terms of physical properties that include color, smell, taste, and texture, and proximate and chemical analyses that include amino acids, fatty acids, minerals, and vitamins. The amino acid profile is usually determined by ion-exchange chromatography or HPLC systems equipped with fluorescent detectors. The fatty acid composition is, in most instances, analyzed via gas chromatography coupled with a flame ionization detector. New capillary columns allow the analysis of fatty acid isomers, such as trans configured, that need to be declared in food labels in many countries around the globe. 

Unsaturated fatty acids can be drawn as cis and trans isomers. For example, oleic acid, a monounsaturated fatty acid found in olives, has one double bond at carbon 9. We can show its cis and trans structures using its skeletal formulas. The cis structure is the more prevalent isomer found in naturally occurring unsaturated fatty acids. In the cis isomer, the carbon chain has a kink at the double bond site. As we will see, the cis bond has a major impact on the physical properties and uses of unsaturated fatty acids. 

Trans bonds have minimal effect on the conformation of the carbon chain such that their physical properties more closely resemble those of saturated fatty acids than of cis unsaturated fatty acids. The conformation remains linear, compared with cis fatty acids, which are kinked (Figure 2). Hence, trans isomers can pack together more closely than their cis counterparts. 

---