FATS and OILS Gülce Güngör 12-C

Fats and Oils Lipids (fats and oils), also known as triglycerides, are esters of glycerol (propan-1,2,3-ol) and fatty acids (long chain carboxylic acids)

Fats and Oils In most oils and fats, the total number of carbon atoms are even because they are synthesised from two carbon units. The groups R1, R2 and R3 represent hydrocarbon chains, typically 15-25 carbon atoms long. These might be different or same. Saturated (All C—C) Mono-unsaturated (Single C=C) Poly-unsaturated (More than one C=C)

Difference Between Fats & Oils They are chemically similar. Main difference is their melting and boiling points. Fats are solid at room temperature and oils are liquid. The melting points and hardness of the solid (degree of crystallinity) depend on several factors.

Factors that affect the physical properties of lipids The mean length of hydrocarbon chains: The greater the carbon chain, the stronger Van der Waals forces, therefore the higher the melting point. The degree of unsaturation: The presence of double bonds reduces the “straightness” of the hydrocarbon chain, therefore reduces the effect of VDW forces. The greater the degree of unsaturation, the lower the melting point.

Whether the hydrocarbon chains is in cis- or trans- form around the double C=C bonds: The effect of double bonds on the “straightness” of the chain is much greater if the chain is in the cis- form than it is in the trans- form. As a result, cis-unsaturated oils have a lower melting point than equivalent trans- ones.

Solid or...? Fatty acids present in mixture affect the properties. Saturated triglycerides pack closely together. Attractive forces - higher melting point.

…or Liquid? Unsaturated triglyceride molecules cannot pack closely together because of cis double bonds - causes kinks! Intermolecular forces are weaker. Less energy needed to separate molecules - lower melting point.

saturated stearic acid m.p. 73 oC “cis” monounsaturated oleic acid m.p. 5.5 oC

Lipids that have saturated hydrocarbon chains tend to be solids at room temperature. (e.g: coconut fat, butter, lard) They form more crystalline solids which are relatively harder. Oils, which are liquid at room temperature, give less crystalline, softer solids when solidified. They are unsaturated. Poly-unsaturated oils (e.g: sunflower oil, corn oil, fish oil) have lower melting points and form softer solids than mono-unsaturated oils (e.g: olive oil, canola oil, peanut oil.)

Reactivity of Fats and Oils Unsaturated oils are less stable and therefore keep less well than saturated fats. The major problem is the rxn of the carbon-carbon double bond with oxygen (auto-oxidation), especially in the presence of light (photo-oxidation), which is why the surface of margarine is often discoloured. Unsaturated lipids are also more likely for hydrogenation and hydrolysis, as well as enzyme-catalysed degradation by microbes.

Unsaturated oils are often hydrogenated using hydrogen at high temperature of about 200°C with catalysts such as nickel to form products that are more / fully saturated.

Advantages and Disadvantages of Hydrogenation The hydrogenation process has some practical advantages: The product is a semi-solid or solid, rather than a liquid, which is more convenient for some cooking techniques. The product is more stable because the rate of oxidation is decreased. The texture (hardness and plasticity) of the product can be controlled.

On the other hand, mono- and poly- unsaturated fats are healthier for the heart. Also partial hydrogenation can lead to the formation of trans-fats, which, as they are not natural, are difficult to metabolise and hence accumulate in the fatty tissues of the body. Trans fats also increases the level of LDL cholesterol, which can lead to atherosclerosis (narrowing of the arteries) and a resultant increase in the probability of strokes and heart problems.