Chemical and Physical properties of Oil and Fat (Unit 2)

designed for undergraduate study

1. Chemical and physical properties of oils and fats 2.1 Structure of lipid and fatty acids 2.2 chemical and biological synthesis of fatty acids and lipid. 2.3 Physical properties 2.4 Chemical properties

2. lipids Lipid is a biomolecule isolated from plant or animal sources by extraction with nonpolar organic solvents, such as diethyl ether and hexane. Lipids are a heterogeneous group of naturally occurring organic compounds (many related to oil and fats). Fats are one type of lipid. They have a number of functions in living systems including that of energy storage. Although carbohydrates serve as a source of readily available energy, an equal weight of fat delivers over twice the amount of energy,

3. It is more efficient for an organism to store energy in the form of fat because it requires less mass than storing the same amount of energy in carbohydrates or proteins. Lipids are insoluble in water but soluble in non-polar aprotic organic solvents, including diethyl ether, dichloromethane, and acetone. Lipids are divided into two main groups. (1) Lipids that contain both a relatively large nonpolar hydrophobic region, most commonly aliphatic in nature, and a polar hydrophilic region. Examples of this type of lipids are, triglycerides, fatty acids , phospholipids, prostaglandins, and the fat-soluble vitamins. (2) Lipids that contain the tetracyclic ring system called the steroid nucleus, including cholesterol, steroid hormones, and bile acids.

4. Lipid can be categorized in the following groups: Fatty acids (saturated and unsaturated) Glycerides (glycerol containing lipids) Nonglycerides lipids (sphingolipids, steroids, waxes) Complex lipids (lipoprotein, glycolipids)

5. triglycerides Triglyceride (triacylglycerol) is ester of glycerol with three fatty acids. In animal fats and vegetable oils, the most abundant naturally occurring lipids are triesters of glycerol and long-chain carboxylic acids. Fats and oils are also referred to as triglycerides or triacylglycerols. Hydrolysis of a triglycerides in aqueous base followed by acidification gives glycerol and three fatty acids.

6. Fats and oils are naturally occurring mixtures of triacylglycerols also called triglycerides. They differ in that fats are solid at room temperature and oils are liquids. All three acyl groups in a triacylglycerol may be the same, all three may be different, or one may be different from the other two. Structure of lipid

7. Difference in triglycerides and phospholipid structures

8. Natural occurring cocoa butter lipid Example of two natural occurring lipids found in cocoa butter., (a) 2-oleyl-1,3-distearylglycerol, (b) tristearin. Hydrogenation of 2-oleyl-1,3-distearylglycerol gives tristrearin . Hydrogenation raise the melting point from 43 °C in 2-oleyl-1,3-distearylglycerol to 72 °C in tristrearin .

9. Structure of Other lipids

10. Structure of Other lipids (waxes)

11. Structure of Other lipids (lipoprotein)

12. fatty acids More than 500 different fatty acids have been isolated from various cells and tissues. Nearly all natural occurring fatty acids have an even number of carbon atoms, most between 12-and 20, in an unbranched chain. The three most abundant fatty acids in nature are palmitic acid (16:0), stearic acid (18:0), and oleic acid (18:1). In most unsaturated fatty acids, the cis isomer predominates; the trans is rare. Unsaturated fatty acids have lower melting points than their saturated counterparts. Fatty acids do not dissolve in water. Longer chains of fatty acids gives more hydrophobic nature, less water soluble. The greater the degree of unsaturation, the lower the melting point. Increase of number of double bonds in fatty acid chain increase the solubility

13. Common fatty acids

14. Structure of fatty acids Fatty acids can be classified as: Saturated fatty acids Unsaturated fatty acids

15. Structure of fatty acids

16. Saturated fatty acids Contain only single bonded carbon chain. Closely packed structure. Strong attractions between chains. High melting points. Solid at room temperature. Common  Name IUPAC Name MP o C RCOOH Formula Condensed Formula Capric Decanoic   32 C 9 H 19 COOH CH 3 (CH 2 ) 8 COOH Lauric Dodecanoic 44 C 11 H 23 COOH CH 3 (CH 2 ) 10 COOH Myristic Tetradecanoic 54 C 13 H 27 COOH CH 3 (CH 2 ) 12 COOH Palmitic Hexadecanoic 63 C 15 H 31 COOH  CH 3 (CH 2 ) 14 COOH Stearic Octadecanoic 70 C 17 H 35 COOH CH 3 (CH 2 ) 16 COOH  Arachidic Eicosanoic 77 C 19 H 39 COOH CH 3 (CH 2 ) 18 COOH

17. Unsaturated fatty acids Contains one or more C=C bonds with cis configuration. It can be hydrogenated. The presence of double bond causes restrictions in the rotation along the bond. The cis-form configuration gives a kink in the molecular shape and less stable than the trans-form. Nonlinear chains do not allow molecules to pack closely. Few interactions between chains. Low melting points. Liquids at room temperature Common Names I.U.P.A.C Name MP o C RCOOH Formula # of Double Bonds Double Bond Position Palmitoleic cis-9-Hexadecenoic C 15 H 29 COOH 1 9 Oleic  cis-9-Octadecnoic 16 C 17 H 33 COOH  1 9 Linoleic  cis,cis-9,12-Octadecadienoic 5 C 17 H 33 COOH  2 9, 12 Linolenic All cis-9,12,15-Octadecatrienoic -11 C 17 H 31 COOH  3 9, 12, 15 Arachidonic All cis-5,8,11,14-Octadecatrienoic -50 C 19 H 31 COOH  4 5, 8, 11, 14

18. Chemical and biological synthesis of fatty acids and lipid Fatty acids are biosynthesized by way of acetyl coenzyme A. The major elements of fatty acids biosynthesis by considering the formation of butanoic acid from two molecules of acetyl coenzyme A. The conversion reaction accomplish with a complex enzymes known as fatty acid synthetase. Certain portions of this complex, referred to as acyl carrier protein (ACP), bear a side chain that is structurally similar to coenzyme A. An important early step in fatty acid biosynthesis is the transfer of the acetyl group from a molecules of acetyl coenzyme A to the sulfhydryl group of acyl carrier protein.

19. Net reaction

20. Physical properties of oil and fat Physical properties of a triglyceride depend on its fatty acid components. The melting point of a triglyceride increases as the number of carbons in its hydrocarbon chains increases and as the number of carbon-carbon double bonds decreases. Triglycerides rich in oleic acid, linoleic acid, and other unsaturated fatty acids are generally liquids at room temperature and are called oils, e.g. corn oil, olive oil. Olive oil, which contains mainly the mono-unsaturated oleic acid, solidifies in the refrigerator, where as the more unsaturated corn oil will not. Triglycerides rich in palmitic, stearic, and other saturated fatty acids are generally semisolids or solids at room temperature and are called fats, e.g. human fat and butter fat. Fats of land animals typically contain approximately 40-50% saturated fatty acids by weight. Most plant oils on the other hand contain 20% or less saturated fatty acids and 80% or more unsaturated fatty acids. Exception of plant oils are tropical oils such as coconut and palm oils, which are considerably richer in low-molecular weight saturated fatty acids.

21. Freshly prepared fats and oils are colorless, odorless and tasteless. Any color or taste is due to association with foreign substances. Fats have specific gravity less than 1 and therefore they float on water. Fats are insoluble in water but soluble in organic solvents as ether and benzene. Melting points of fats are usually low but higher that solidification point.

22. Chemical properties of lipids Hydrolysis They are hydrolyzed into their constituents (fatty acids and glycerol) by the action of superheated steam, acid, alkali or enzyme During enzymatic and acid hydrolysis, glycerol and free fatty acids are produced

23. Saponification Alkaline hydrolysis produces glycerol and salts of fatty acids Soap cause emulsification of oily material this help easy washing of fatty materials

24. Halogenation Neutral fats containing unsaturated fatty acids have the ability of adding halogens at the double bonds It is a very important property to determine the degree of unsaturation of the fat or oil that determines its biological value.

25. Hydrogenation or hardening of oils It is a type of addition reactions accepting hydrogen at the double bonds of unsaturated fatty acids. The hydrogenation is done under high pressure of hydrogen and is catalyzed by finely divided nickel or copper and heat. It is the base of hardening of oils (margarine manufacturing), e.g., change of oleic acid of fats (liquid) into stearic acid (solid). It is advisable not to saturate all double bonds; otherwise margarine produced will be very hard, of very low biological value and difficult to digest.

26. Advantages of hydrogenated: It is more pleasant as cooking fat. It is digestible and utilizable as normal animal fats and oils. It is less liable to cause gastric or intestinal irritation. It is easily stored and transported and less liable to rancidity. Disadvantages of hydrogenated: fats include lack of fat-soluble vitamins (A, D, E and K) and essential fatty acids

27. Oxidation (Rancidity) This toxic reaction of triglycerides leads to unpleasant odour or taste of oils and fats developing after oxidation by oxygen of air, bacteria, or moisture. Also this is the base of the drying oils after exposure to atmospheric oxygen. Example is linseed oil, which is used in paints and varnishes manufacturing Definition: It is a physico-chemical change in the natural properties of the fat leading to the development of unpleasant odor or taste or abnormal color particularly on aging after exposure to atmospheric oxygen, light, moisture, bacterial or fungal contamination and/or heat. Saturated fats resist rancidity more than unsaturated fats that have unsaturated double bonds.

28. Types and causes of rancidity Hydrolytic rancidity Oxidative rancidity Ketonic rancidity

29. 1. Hydrolytic rancidity It results from slight hydrolysis of the fat by lipase from bacterial contamination leading to the liberation of free fatty acids and glycerol at high temperature and moisture. Volatile short-chain fatty acids have unpleasant odor.

30. 2. Oxidative rancidity It is oxidation of fat or oil catalyzed by exposure to oxygen, light and/or heat producing peroxide derivatives which on decomposition give substances, e.g., peroxides, aldehydes, ketones and dicarboxylic acids that are toxic and have bad odor. This occurs due to oxidative addition of oxygen at the unsaturated double bond of unsaturated fatty acid of oils.

31. 3. Ketonic rancidity It is due to the contamination with certain fungi such as Asperigillus Niger on fats such as coconut oil. Ketones, fatty aldehydes, short chain fatty acids and fatty alcohols are formed. Moisture accelerates ketonic rancidity.

32. Prevention of rancidity Avoidance of the causes ( exposure to light, oxygen, moisture, high temperature and bacteria or fungal contamination ). By keeping fats or oils in well-closed containers in cold, dark and dry place (i.e., good storage conditions). Removal of catalysts such as lead and copper that catalyze rancidity. Addition of anti-oxidants to prevent peroxidation in fat (i.e., rancidity). They include phenols, naphthols , tannins and hydroquinones . The most common natural antioxidant is vitamin E that is important in vitro and in vivo .

33. Hazards of rancid fats The products of rancidity are toxic, i.e., causes food poisoning and cancer. Rancidity destroys the fat-soluble vitamins (vitamins A, D, K and E). Rancidity destroys the polyunsaturated essential fatty acids. Rancidity causes economical loss because rancid fat is inedible.

34. Slides ends here Thanks for your patience.