Practial Report

Degree of Saturation:

Iodine number and Saponification

Chanel van Reede van Oudtshoorn

16751531

Department of Biochemistry

06/09/2013

Introduction:

Free fatty acids are present in small amounts in the living cell (horton). The general formula is R-COOH, where the R-group is the hydrocarbon chain and the COOH-group is the carboxylic acid. The hydrocarbon chain is composed of a variety of lengths of methylene-units (-CH2) (horton). By means of an ester bond between a glycerol and a fatty acid backbone, a lipid is produced. Lipids come in many forms and serve many functions. Sub lipids are Triacylglycerols (TAG), Shingolipids and Glycerophospholipids. In this experiment the focus is on Triacylglycerols.

Structural change in lipids is as a result of the degree of saturation. Saturation depends on the amounts of double bonds the fatty acid has. C-C double bonds also differ in amount and placement. When there are no carbon-carbon double bonds present then the lipid is saturated. When, however, there is one double bond the lipid is monounsaturated and when there are more than two double bonds the lipid is polyunsaturated. Together with these structural differences comes change in physical properties.

A saturated lipid takes form of a solid at room temperature, while an unsaturated lipid has a liquid form at room temperature. This, of course, affects the melting point of each lipid respectively. Thus, the degree of saturation must be calculated. This can be done by calculating the total grams of I2 that saturates 100g if lipid. This is known as the Iodine number (notes).

By adding excess Iodine to a lipid and then allowing it to bond to the double bond in the fatty acid chain, one can determine, through titration with a reducing agent Na2S2O3, the amount of Iodine (I2) that is left. Then one can determine the amount of Iodine bound to the lipid by doing a simple calculation.

The degree of saturation depends on not only the Iodine number, but also the...