THE CHEMISTRY OF LIPID
The Chemistry of Lipids
Experiment #8
Objective
To observe the solubility of lipids in polar and nonpolar solvents and to compare saturated and unsaturated fats in their chemical reaction with bromine. The percent fat in a food will be determined by extraction of the fat and weighing it.
Introduction
Lipids, by definition, are natural substances that do not mix with water but dissolve in organic solvents. There are several classes of lipids, including: fatty acids, waxes, triacylglycerols (fats and oils), phospholipids and steroids. The fatty acids are usually not free in nature, but are components of triacylglycerols, waxes and phospholipids. Animal fats or vegetable oils (especially palm oil) are used to make soap. You prepared soap in an earlier experiment. Fatty acids are classified as saturated or unsaturated, according to whether they have carbon-carbon double bonds or not. The carbon-carbon double bonds are sites where the molecules are not saturated with hydrogen and are susceptible to chemical attack. One substance that readily attacks these double bonds is the element bromine (Br2). The product of this reaction is a brominated fatty acid (see the reaction below). One measure of the degree of unsaturation of fats and oils used by food chemists is known as the iodine number, where iodine is used in place of bromine for this reaction.
H3C(CH2)16COOH
+
Br2
No Reaction
H H
H H
H3C(CH2)7 C C (CH2)7COOH
+
H3C(CH2)7 C C (CH2)7COOH
Br2
Br Br
Phospholipids, such as lecithin, have a polar or charged portion and a nonpolar portion consisting of the long chain fatty acids within the same molecule. Consequently the polar or charged portion of these molecules will mix with water and the nonpolar portion repels the water but mixes with lipids.
Phosphatidyl Choline (Lecithin)
o
Nonpolar Tail
o
O CH2
O CH
Polar Head
o
CH2OPOCH2CH2N(CH3)3+
o-
63
.
These phospholipids will form
Experiment #8
Objective
To observe the solubility of lipids in polar and nonpolar solvents and to compare saturated and unsaturated fats in their chemical reaction with bromine. The percent fat in a food will be determined by extraction of the fat and weighing it.
Introduction
Lipids, by definition, are natural substances that do not mix with water but dissolve in organic solvents. There are several classes of lipids, including: fatty acids, waxes, triacylglycerols (fats and oils), phospholipids and steroids. The fatty acids are usually not free in nature, but are components of triacylglycerols, waxes and phospholipids. Animal fats or vegetable oils (especially palm oil) are used to make soap. You prepared soap in an earlier experiment. Fatty acids are classified as saturated or unsaturated, according to whether they have carbon-carbon double bonds or not. The carbon-carbon double bonds are sites where the molecules are not saturated with hydrogen and are susceptible to chemical attack. One substance that readily attacks these double bonds is the element bromine (Br2). The product of this reaction is a brominated fatty acid (see the reaction below). One measure of the degree of unsaturation of fats and oils used by food chemists is known as the iodine number, where iodine is used in place of bromine for this reaction.
H3C(CH2)16COOH
+
Br2
No Reaction
H H
H H
H3C(CH2)7 C C (CH2)7COOH
+
H3C(CH2)7 C C (CH2)7COOH
Br2
Br Br
Phospholipids, such as lecithin, have a polar or charged portion and a nonpolar portion consisting of the long chain fatty acids within the same molecule. Consequently the polar or charged portion of these molecules will mix with water and the nonpolar portion repels the water but mixes with lipids.
Phosphatidyl Choline (Lecithin)
o
Nonpolar Tail
o
O CH2
O CH
Polar Head
o
CH2OPOCH2CH2N(CH3)3+
o-
63
.
These phospholipids will form