Determination of Saponification and Iodine Number of Some Lipids

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  • Topic: Fatty acid, Fat, Saponification
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DETERMINATION OF SAPONIFICATION AND IODINE NUMBERS OF SOME LIPIDS

A.L. ASCANO1 C.V. OPONDA1
1INSTITUTE OF BIOLOGY
UNIVERSITY OF THE PHILIPPINES, DILIMAN, QUEZON CITY, PHILIPPINES DATE PERFORMED: FEBRUARY 19, 2013
INSTRUCTOR’S NAME: FRANCESCA N. BELTRAN

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ABSTRACT
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INTRODUCTION

Lipids are long aliphatic hydrocarbon chains which are either branched or unbranched that can form rings and may have unsaturation. [8] They are products of animal or vegetable origin which are extracted with either ether, chloroform, benzene, petroleum, carbon disulfide. [6] They can be described as substances which are insoluble in water but soluble in fat solvents. [5] Lipids are compounds that share properties based on their structural similarities mainly a preponderance of nonpolar groups. [4] It includes compounds such as fatty acids, glycerolipids, sphingolipids, terpenes, steroids and carotenoids. [7]

Lipids can be classified as: saponifiable lipids and unsaponifiable lipids. Saponifiable lipids are open-chain compounds containing polar heads and long nonpolar chains. Among the saponifiable lipids are triacylglycerols, waxes, sphingolipids and phospholipids. Unsaponifiable lipids on the other hand are those with fused rung compounds such as steroid and cholesterol. [8]

Molecular weight can be calculated by

MW= (3 x g sample)/(mol KOH)(1)

Lipids of natural origin are usually obtained from their esters by alkaline hydrolysis. Such procedures allow the yield of complex mixtures of fatty acids which are resolvable with relative difficulty. Description of fatty acids therefor is restricted to the determination of its average chain length, average degree of unsaturation. Measurement of such characteristics is done through both chromatographic and chemical methods of analysis. Chemical methods include the determination of: Saponification Number, Iodine Number, Acid Number, Total Fatty Acids, Reichert-Meissl Number, Helner Number, Polenske Number, Acetyle Number, Thiocyanogen Number, Titration Equivalent Weight. [5,6]

Saponification Number is the measure of the average molecular weight of triacylglycerol in the sample.[9] It determines the amount of potassium hydroxide necessary to saponify one gram of oil. [5] Saponification involves the decomposition of neutral fats by subjecting them to the action of an alkali. [10]

Saponification value can be calculated by

SN= (mg KOH)/(g sample)(2)

Iodine Number determination looks into the fact that double bond react quantitatively with Br2, I2 and IBr at room temperature in acetic acid or pyridine solution. [6] It therefore determines the degree if unsaturation of a lipid. It dictates how much iodine was taken up by 1 gram of fat. [5] Iodine monochloride is added allowing to occur. Unconsumed ICI is determined by titrating excess potassium iodine. Liberated iodine is reacted with sodium thiosulphate. Difference in the amount of ICI consumed by the unsaturation present is found out which will give a measure of the unsaturation present. [10] Reaction is given by:

Iodine number is given by:

IN=100 x (g I_2)/(g sample)(3)

Acid Number measures the amount of free acid present in a given amount of fat. It determines how much KOH is necessary to neutralize the fatty acid of one gram of the lipid. [10] Total fatty acid determines the amount of fatty acid present by extraction through saponification and drying with lead acetate solution. [5] Reichert-Meissl Number determines the amount of 0.1N potassium hydroxide required to neutralize the volatile acid from five grams of saponified fat or oil. [5] Helner number is the weight of insoluble fatty acids yielded by five grams of saponified fat or oil. Polske Nmber determines the amount of 0.1N potassium hydroxide required...
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