Lab Activity 5Lab Activity 5LipidsLipids

Alaa BarakaAlaa BarakaIUGIUGMarch2013March2013

LipidsLipidsLipids are are

Biomolecules that contain fatty acids or a Biomolecules that contain fatty acids or a steroid nucleus.steroid nucleus.Soluble in organic solvents but not in Soluble in organic solvents but not in water.water.Named for the Greek word Named for the Greek word liposlipos, which , which means “fat.”means “fat.”Extracted from cells using organic Extracted from cells using organic solvents.solvents.

Classification of Lipids1. Simple LipidsA. Neutral fats - TriglyceridesB. Waxes

2. Conjugated Lipids (polar lipids)A. Phospholipids - contain a phosphoric acid molecule and a fat molecule.B. Glycolipid- contain a carbohydrate and a fat molecule.C. Sulfolipids - contain a sulfate radical.D. lipoprotein

3. Derived LipidsA. Fatty acidsB. GlycerolC. Cholesterol and other steroid (Vit. D)D. Vitamins A, E, K

ExamplesExamples

1.1. ButterButter2.2. GheeGhee3.3. LardLard4.4. TallowsTallows5.5. Vegetabels oilsVegetabels oils6.6. PhospholipidsPhospholipids7.7. SphengolipidsSphengolipids8.8. TerpenoidsTerpenoids9.9. SteroidsSteroids

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Fatty AcidsFatty Acids

Fatty acidsFatty acids Are long-chain Are long-chain carboxylic acids.carboxylic acids.Typically contain 12-Typically contain 12-18 carbon atoms.18 carbon atoms.Are insoluble in water.Are insoluble in water.Can be saturated or Can be saturated or unsaturated.unsaturated.

Lab ActivityLab Activity::

Solubility in Polar and Non-polar SolventsEmulsification

Lecithin as Emulsifying AgentLecithin as Emulsifying AgentRancidityRancidityAcid Value DeterminationAcid Value Determination

1. Solubility in Polar and Non-polar Solvents

• Reagents • Olive oil (vegetable oil), butter (animal fat), • stearic acid (saturated fatty acid), oleic acid (unsaturated

fatty acid), • Solvents: dilute acid and alkali solutions, cold alcohol,

hot alcohol, benzene, chloroform, ether and carbon tetrachloride.

•  • Procedure

1. Add a few drops of the liquid fat or 0.1 g of the solid fat in labeled test tubes.

2. To each test tube add a 1 ml of solvent and write down your observations.

3. Repeat the experiment with a different solvent and make your observations.

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2. Emulsification

Reagents• Neutral olive oil, 0.5 % Na2C03, Rancid olive oil

Procedure1. Shake up a drop of neutral olive oil with a little water in a test

tube, the fat becomes finally divided forming an emulsion, upon standing fat separates and rises to the top.

2. To 5 ml water in a test tube add 2 to 3 drops of 0.5 percent Na2CO3. Introduce a drop of neutral olive oil and shake, the emulsion is not permanent and is not so transitory.

3. Repeat step 2 using rancid olive oil. In this case the alkali combines with the free fatty acids to form soap and the soap being an emulsifying agent, it emulsifies the fat.

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33 . .Lecithin as Emulsifying AgentLecithin as Emulsifying Agent

Lecithin (phosphatidyl choline) is present Lecithin (phosphatidyl choline) is present in nerve, brain and other tissues of in nerve, brain and other tissues of animals, plants.animals, plants.Egg yolk contains lecithin.Egg yolk contains lecithin.Lecithin has a polar head (ionic) and 2 Lecithin has a polar head (ionic) and 2 nonpolar hydrocarbon tails (fatty acid nonpolar hydrocarbon tails (fatty acid units) which make it an excellent units) which make it an excellent emulsifying agent.emulsifying agent.

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ProcedureProcedure

A. Preparation of lecithin:A. Preparation of lecithin:- Place an egg yolk in a 250 ml Erlenmeyer Place an egg yolk in a 250 ml Erlenmeyer

flask, add 50 ml of ether, shake vigorously.flask, add 50 ml of ether, shake vigorously.- Filter the mixture through a dry paper into a Filter the mixture through a dry paper into a

beaker and evaporate the ether on a steam-beaker and evaporate the ether on a steam-heated sand bath or water-bath.heated sand bath or water-bath.

- Cool the solution, then add about 25 ml of Cool the solution, then add about 25 ml of acetone, stir until the precipitate clumps and acetone, stir until the precipitate clumps and sticks to the beaker, then pour off the sticks to the beaker, then pour off the acetone.acetone.

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- Transfer ½ of the precipitate to a test tube, Transfer ½ of the precipitate to a test tube, add 1 ml of water and 1 ml of vegetable add 1 ml of water and 1 ml of vegetable oil, stopper the tube and shake very oil, stopper the tube and shake very vigorously.vigorously.

- Repeat the above step in another test tube Repeat the above step in another test tube but without lecithin. Compare the two test but without lecithin. Compare the two test tubes. After 5 mintubes. After 5 min

- Make your commentsMake your comments

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RANCIDITYRANCIDITY

What is rancidityWhat is rancidity??Rancidity is the development of Rancidity is the development of unpleasant smells in fats and oilsunpleasant smells in fats and oils, , which which are often accompanied by changes in their are often accompanied by changes in their texture and appearancetexture and appearance..Two types of Two types of rancidityrancidity::Hydrolytic rancidity Oxidative Hydrolytic rancidity Oxidative rancidityrancidity((autoauto--oxidationoxidation))

Hydrolytic rancidityHydrolytic rancidityOxidative rancidityOxidative rancidity

CausedbythebreakingdownofaliCausedbythebreakingdownofalipidintoitscomponentfattyacidsanpidintoitscomponentfattyacidsandglyceroldglycerol..CC--OO--COCO--RR++HH22OO→→CC--OO--HH++HOHO--COCO--RR

OccursduetotheoxidationoffattyOccursduetotheoxidationoffattyacidchainsacidchains,,typicallybytheadditiotypicallybytheadditionofoxygenacrosstheCnofoxygenacrosstheC==CbondinCbondinunsaturatedfattyacidsunsaturatedfattyacids. .

Occurs more rapidly in the Occurs more rapidly in the presence of enzymes such presence of enzymes such as lipaseas lipase, , and withand with heat heat and moistureand moisture

The process proceeds by The process proceeds by afree radical afree radical mechanismcatalysedbylightmechanismcatalysedbylightinthepresenceofenzymesorinthepresenceofenzymesormetal ionsmetal ions

44 . .RancidityRancidity

ReagentsReagentsFresh olive oil, Fresh olive oil, rancid olive oil, rancid olive oil, oleic acid, oleic acid, litmus paperlitmus paper

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ProcedureProcedure

Try the reaction of fresh olive oil, oleic acid Try the reaction of fresh olive oil, oleic acid to litmus paper.to litmus paper.Repeat the test with rancid oil.Repeat the test with rancid oil.What is the reaction of a fresh lipid and What is the reaction of a fresh lipid and that of rancid lipid?that of rancid lipid?

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55 . .Acid Value (free fatty acids) Acid Value (free fatty acids) DeterminationDetermination

Acid valueAcid value is a measure of the extent to which is a measure of the extent to which the glycerides have been hydrolyzed by a lipase the glycerides have been hydrolyzed by a lipase action. Hydrolysis is accelerated by heat and action. Hydrolysis is accelerated by heat and light.light.Acid value is an index of the efficiency of oil Acid value is an index of the efficiency of oil refining during which the free fatty acids are refining during which the free fatty acids are removed and the acid value falls to very low removed and the acid value falls to very low values.values.Rancidity is usually accompanied by formation Rancidity is usually accompanied by formation of free fatty acids (indication of a deterioration of of free fatty acids (indication of a deterioration of oils in storage conditions)oils in storage conditions)

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MaterialsMaterials

Oil sample,Oil sample,0.1 N KOH0.1 N KOH1% phenolphthalein solution1% phenolphthalein solutionEtherEtherEthanolEthanol250 Erlenmeyer flask250 Erlenmeyer flaskburetteburette

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ProcedureProcedure

1. Mix 25 ml of ether with 25 ml of ethanol, and 1. Mix 25 ml of ether with 25 ml of ethanol, and 1-2 drops phenolphthalein in an erlenmeyer 1-2 drops phenolphthalein in an erlenmeyer flaskflask2. Neutralize the mixture with 0.1N KOH2. Neutralize the mixture with 0.1N KOH3. Dissolve 25 g of the oil in the mixed neutral 3. Dissolve 25 g of the oil in the mixed neutral solvent.solvent.4. Titrate with 0.1 N KOH, shaking constantly 4. Titrate with 0.1 N KOH, shaking constantly until pink color which persists for 15 sec.until pink color which persists for 15 sec.Calculate the acid value and the percentage of Calculate the acid value and the percentage of free fatty acid in the tested samplefree fatty acid in the tested sample..

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CalculationsCalculations

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