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FATS and OILS

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.

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FATS and OILS

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  1. FATS and OILS Gülce Güngör 12-C

  2. 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)

  3. FatsandOils • Inmostoilsandfats, the total number of carbonatomsareevenbecausetheyaresynthesisedfromtwocarbonunits. • Thegroups R1, R2and R3 representhydrocarbonchains, typically 15-25 carbonatomslong. Thesemight be differentorsame. • Saturated (All C—C) • Mono-unsaturated (Single C=C) • Poly-unsaturated (Morethanone C=C)

  4. DifferenceBetweenFats & 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.

  5. Factorsthataffectthephysicalproperties of lipids • Themeanlength of hydrocarbonchains:Thegreaterthecarbonchain, thestronger Van der Waalsforces, thereforethehigherthemeltingpoint. • Thedegree of unsaturation:The presence of doublebondsreducesthe “straightness” of thehydrocarbonchain, thereforereducestheeffect of VDW forces. Thegreaterthedegree of unsaturation, thelowerthemeltingpoint.

  6. Whetherthehydrocarbonchains is in cis- ortrans- form aroundthedouble C=C bonds: Theeffect of doublebonds on the “straightness” of thechain is muchgreaterifthechain is in thecis- form than it is in thetrans- form. As a result, cis-unsaturatedoilshave a lowermeltingpointthanequivalent trans- ones.

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

  8. …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.

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

  10. Lipidsthathavesaturatedhydrocarbonchainstendto be solids at roomtemperature. (e.g: coconutfat, butter, lard) They form morecrystallinesolidswhicharerelativelyharder. • Oils, whichareliquid at roomtemperature, givelesscrystalline, softersolidswhensolidified. Theyareunsaturated. • Poly-unsaturatedoils (e.g: sunfloweroil, cornoil, fishoil) havelowermeltingpointsand form softersolidsthan mono-unsaturatedoils (e.g: oliveoil, canolaoil, peanutoil.)

  11. Reactivity of FatsandOils • Unsaturatedoilsarelessstableandthereforekeeplesswellthansaturatedfats. • Themajor problem is therxn of thecarbon-carbondoublebondwithoxygen (auto-oxidation), especially in the presence of light (photo-oxidation), which is whythesurface of margarine is oftendiscoloured. • Unsaturatedlipidsarealsomorelikelyforhydrogenationandhydrolysis, as well as enzyme-catalyseddegradationbymicrobes.

  12. 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.

  13. AdvantagesandDisadvantages 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.

  14. 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.

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