Fats and oils

Introduction

Lipids are sometimes classified loosely as those water-insoluble organic substances which can be extracted from cells by organic solvents. They cannot be defined precisely because their chemistry is so variable. True lipids can be said to be formed by condensation reactions between fatty acids an an alcohol.

The lipid family is very large and diverse. It includes cholesterol, hormones, and the edible fats and oils we eat.

Fats and oils are composed of two basic parts; glyceride and fatty acids.

Fatty acid structure is generally as follows

CH₃(CH₂)nCOOH

Fatty acids differ in many ways. A primary difference is chain length. Generally they are categorized as seen in the table below.

Fatty acids are also categorized as:

1. Saturated: carbon atoms have all the hydrogen atoms that will combine with them

2. Unsaturated: some of the hydrogen atoms are missing from some of the carbons. Degree of unsaturation differs dependent on the number of missing hydrogens.

NOTE: the ratio of saturated to unsaturated fatty acid has a major impact on whether something is a fat or an oil.

Constituents of lipids

1.Fatty acids

Fatty acids contain the acidic group-COOH (the carboxyl group) and are so named because some of the larger molecules in the series occur in fats. They have the general formula R.COOH. There are usually many carbon atoms in the fatty acids used to make lipids. Most naturally occurring fatty acids have an even no. of carbon atoms between 14 & 22 (most commonly 16 or 18). The characteristically long chain of carbon and hydrogen atoms forming a hydrocarbon tail. These tails, including their insolubility in water determine many of the properties of lipids. The tails are said to be hydrophobic, meaning water hating (hydro, water; phobos, fear).

Over 1/2 of plant and animal fatty acids are unsaturated, plant lipids tending to be more unsaturated than their animal counterparts

Double bonds impart some special characteristics to the unsaturated fatty acids. Remember that the presence of double bonds raises the possibility of geometric isomerism. Unsaturated fatty acids may be either cis or trans isomers.

2.Glycerol

Propane-1,2,3-triol (glycerol)

3.Structure

Usually Glycerol has 3 groups, all of which can condense with a fatty all 3 undergo condensation reactions as shown below, and the lipid formed is therefore called a triglyceride.

Chemically, fats and oils are esters of glycerol and the higher molar mass fatty acids. They have the general formula where R? s can be either long-chain saturated or unsaturated hydrocarbon groups. The gragh on the left shows a 3D representation of typical fat.

Fats may be considered to be triesters formed from the trihydroxyl alcohol glycerol and 3 molecules of fatty acids. Most of the fatty acids in these esters have 14 to 18 carbons. Because there are 3 ester groups per glycerol, these molecules are called triacylglycerols, or triglycerides. The 3 R groups are usually different.

Fats and oils fit the general description of a lipid. They are large molecules, averaging more than 50 carbon atoms per molecule, with many nonpolar, uncharged groups. Because they contain large no. of saturated carbons, the triacylglycerols are hydrophobic and water insoluble.

Characteristics and Main Reactions

Other reactions

Food Tests

What is "iodine value"?