Lab Activity 6Lab Activity 6LipidsLipids

Alaa Alaa BarakaBaraka

IUGIUG

March201March20133

Lab ActivityLab Activity

Peroxide value determination.Peroxide value determination.Formation of Acrolein.Formation of Acrolein.Saponification.Saponification.

Marker of rancide oilMarker of rancide oil

Hydrolysis of ester Bond .Hydrolysis of ester Bond .Oxidation of Fatty Acid .Oxidation of Fatty Acid .Formation of carbonyl compound .Formation of carbonyl compound .

A)A) Peroxide Value DeterminationPeroxide Value Determination(iodometric titration)(iodometric titration)

Peroxide value is the concentration of (-O-Peroxide value is the concentration of (-O-O-) groups in edible oils,O-) groups in edible oils,

It is a measurement of the decomposition It is a measurement of the decomposition of the product and in many countries, of the product and in many countries, official standards specify a maximum official standards specify a maximum peroxide number beyond which the oil is peroxide number beyond which the oil is unfit for human consumption.unfit for human consumption.

Formation of peroxide during storage of oil Formation of peroxide during storage of oil or fat may occur after few weeks to or fat may occur after few weeks to several months according to the several months according to the conditions of storageconditions of storage

The peroxide number is therefore The peroxide number is therefore measured by oil manufacturers measured by oil manufacturers during production and after storage during production and after storage to check its preservation. to check its preservation.

International standards use a redox International standards use a redox titration in non‐aqueous media, titration in non‐aqueous media, results are generally expressed in μg results are generally expressed in μg of peroxide (or active oxygen) per of peroxide (or active oxygen) per gram of product but mmoles/kg or gram of product but mmoles/kg or

meq of Omeq of O22/kg are also used./kg are also used.

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Peroxide value is determined Peroxide value is determined volumetricallyvolumetrically

Reaction of KI in acid solution with the Reaction of KI in acid solution with the bound oxygen followed by titration of the bound oxygen followed by titration of the liberated Iliberated I22 with sodium thiosulfate. with sodium thiosulfate.

Chloroform is used as a solvent.Chloroform is used as a solvent. Fresh oil has peroxide value below 10 Fresh oil has peroxide value below 10

meq/kg. meq/kg. Rancid taste often begins to develop when Rancid taste often begins to develop when

the peroxide value is between 20 & 40 the peroxide value is between 20 & 40 meq/kgmeq/kg

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Peroxide number determination Peroxide number determination involves a two‐step redox reaction: involves a two‐step redox reaction:

1) Reaction of peroxide group with an 1) Reaction of peroxide group with an excess of iodide ion according to: excess of iodide ion according to:

ROOR + 2I-+ 2HROOR + 2I-+ 2H++→2ROH + I→2ROH + I22

2) Titration of Iodine with Na2) Titration of Iodine with Na22SS22OO3 3

solution 0.002N, according to: solution 0.002N, according to:

II22+ 2S+ 2S22OO332‐2‐→2I→2I‐‐+ S+ S44OO66

2‐2‐

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MaterialsMaterials

250 ml Erlenmeyer or volumetric flask250 ml Erlenmeyer or volumetric flaskChloroformChloroformFresh saturated aqueous KI solution Fresh saturated aqueous KI solution

(15g /10 ml H(15g /10 ml H22O) store in darkO) store in darkGlacial acetic acid Glacial acetic acid 0.002 N Thiosulfate0.002 N ThiosulfateStarchStarchOil sampleOil sample

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ProcedureProcedure

1. Weigh 1 to 4 g oil sample into 250 ml flask1. Weigh 1 to 4 g oil sample into 250 ml flask 2. Add 10 ml chloroform, dissolve the oil by 2. Add 10 ml chloroform, dissolve the oil by

swirlingswirling 3. Add 15 ml of glacial acetic acid3. Add 15 ml of glacial acetic acid 4. Add 1 ml of a fresh saturated aqueous KI 4. Add 1 ml of a fresh saturated aqueous KI

solutionsolution 5. stopper the flask, shake for 1 min and place 5. stopper the flask, shake for 1 min and place

the flask for 5 min in dark…the flask for 5 min in dark…Why??Why?? 6. Add about 75 ml distilled, mix and titrate (Vml) 6. Add about 75 ml distilled, mix and titrate (Vml)

the formed Ithe formed I22 with 0.002 N solution of thiosulfate with 0.002 N solution of thiosulfate using starch solution (1%) as indicator.using starch solution (1%) as indicator.

7. Carry out a blank titration (V7. Carry out a blank titration (V00ml) which should ml) which should not exceed 0.5 ml of 0.002 N thiosulfate solutionnot exceed 0.5 ml of 0.002 N thiosulfate solution

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CalculationCalculation

Peroxide value Peroxide value = = (V- V(V- V00) T x 1000 meq/Kg) T x 1000 meq/Kg

Where T is the exact molarity of Where T is the exact molarity of thiosulfate solutionthiosulfate solution

weight of sample (g)

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B) Formation of AcroleinB) Formation of Acrolein

ReagentsReagents::

Olive oil, melted butter, potassium Olive oil, melted butter, potassium bisulfate KHSObisulfate KHSO44 , Schiff’s reagent , Schiff’s reagent

Schiff's reagent is a solution that will Schiff's reagent is a solution that will combine chemically with aldehydes combine chemically with aldehydes to form a bright red product.to form a bright red product.

Glycerol KHSOGlycerol KHSO4 4 acrolein + acrolein + 2H2H22OO

heat

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ProcedureProcedure

1. Place about 1 g powdered KHSO1. Place about 1 g powdered KHSO44

in a clean test tube.in a clean test tube.2. add 3 – 4 drops of olive oil (0.5 g 2. add 3 – 4 drops of olive oil (0.5 g

melted butter) on the salt and heat.melted butter) on the salt and heat.3. Note the irritating odor of acrolein 3. Note the irritating odor of acrolein

aldehyde or aldehyde which will aldehyde or aldehyde which will color a filter paper moistened with color a filter paper moistened with Schiff’s reagent bright redSchiff’s reagent bright red

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C) Saponification (Formation of a C) Saponification (Formation of a soluble soap & insoluble soap)soluble soap & insoluble soap)

ReagentsReagents

Olive oil,Olive oil,cow fat,cow fat,5% KOH solt.5% KOH solt.2% MgSO2% MgSO44 solt. solt.

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ProcedureProcedure

1. add 10 ml of olive oil or 10 g of cow fat 1. add 10 ml of olive oil or 10 g of cow fat in a 250 ml beakerin a 250 ml beaker

2. add 50 ml KOH solt.2. add 50 ml KOH solt. 3. add 150 ml dist. Water3. add 150 ml dist. Water 4. Hydrolyze the lipids by heating the 4. Hydrolyze the lipids by heating the

beaker nearly the boiling point for 3 – 5 beaker nearly the boiling point for 3 – 5 minmin

5. Transfer a few amount of the beaker 5. Transfer a few amount of the beaker content into about 30 ml of dist. Water.content into about 30 ml of dist. Water.

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6. Observe if any saponificaton has 6. Observe if any saponificaton has occurred (indicated by the complete occurred (indicated by the complete solubility of the solution when fall solubility of the solution when fall into a dist. Water).into a dist. Water).

7. To form insoluble soap, add a few 7. To form insoluble soap, add a few mls of 2% MgSOmls of 2% MgSO44 solution to the soap solution to the soap solution, while precipitate indicate solution, while precipitate indicate formation of magnesium salts of formation of magnesium salts of fatty acids (insoluble soap).fatty acids (insoluble soap).

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