Introduction to fats & oils

Introduction to fats & oils

Session Objectives

By the end of this session, students will be able to:

Ø Classify fats & oils

Ø Discuss nomenclature of Fatty acids

Introduction

The word lipid is derived from Greek word lipos meaning fats

Play important role in cellular structure and also have various other biochemical functions

Lipids are the chief concentrated storage form of energy

Lipids are heterogenous group of compounds

Lipids may be regarded as organic substances relatively insoluble in water, soluble in organic solvents (alcohol, ether etc.), actually or potentially related to fatty acids and utilized by the living cells

Unlike the polysaccharides, proteins and nucleic acids, lipids are not polymers. Further, lipids are mostly small molecules

• Made from esters of propane-1,2,3,triol(glycerol) + long chain carboxylic acids RCOOH.

• Common fatty acids

Classification of lipids

Lipids are broadly classified into simple, complex, derived and miscellaneous lipids, which are further subdivided into different groups

1) Simple lipids: esters of fatty acids with alcohols

These are mainly of two types

A) Fats and oils B) waxes

A) Fats and oils:

· Are esters of fatty acids with glycerol

· The difference between fat and oil is only physical

· Oil is a liquid while fat is a solid at room temperature

B) Waxes

· Esters of fatty acids (usually long chain) with alcohols other than glycerol

· These alcohols may be aliphatic or alicyclic

· Cetyl alcohol is most commonly found in waxes

2) Complex (or Compound) lipids

These are esters of fatty acids with alcohols containing additional groups such as phosphate, nitrogenous base, carbohydrate, protein etc.

They are further divided as follows

(a) Phospholipids: Contain phosphoric acid and frequently a nitrogenous base, This is in addition to alcohol and fatty acids.

Types of Phospholipids

(i) Glycerophospholipids:

These phospholipids contain glycerol as the alcohol

Eg: lecithin, cephalin

(ii) Sphingophospholipids:

Sphingosine is the alcohol in this group of phospholipids

Eg: sphingomyelin

(b) Glycolipids: These lipids contain a fatty acid, carbohydrate and nitrogenous base.

· The alcohol is sphingosine, hence they are also called as glycosphingolipids.

· Glycerol and phosphate are absent e.g., cerebrosides, gangliosides

(d) Other complex lipids: Sulfolipids, aminolipids and lipopolysaccharides are among the other complex lipids.

3) Derived lipids: These are the derivatives obtained on the hydrolysis of group 1 and group 2 lipids which possess the characteristics of lipids

These include glycerol and other alcohols, fatty acids, mono- and diacylglycerols, lipid (fat) soluble vitamins, steroid hormones, hydrocarbons and ketone bodies

4) Miscellaneous lipids: These include a large number of compounds possessing the characteristics of lipids

Eg: carotenoids, squalene, hydrocarbons such as pentacosane (in bees wax), terpenes etc.

Neutral Lipids: The lipids which are uncharged are referred to as neutral lipids

These are mono-, di-, and triacylglycerols, cholesterol and cholesteryl esters

Fatty acids

· Fatty acids are carboxylic acids with hydrocarbon side chain

· They are the simplest form of lipids

Occurrence:

· Fatty acids mainly occur in the esterified form as major constituents of various lipids

· They are also present as free (unesterified) fatty acids

· Fatty acids of animal origin are much simpler in structure in contrast to those of plant origin

· Contain groups such as epoxy, keto, hydroxy and cyclopentane rings

· Even and odd carbon fatty acids

· Most of the fatty acids that occur in natural lipids are of even carbons (usually 14C- 2OC)

· This is due to the fact that biosynthesis of fatty acids mainly occurs with the sequential addition of 2 carbon units

· Palmitic acid (l6C) and stearic acid (l8C) are the most common

· Among the odd chain fatty acids, propionic acid (3C) and valeric acid (5C) are well known

Saturated and Unsaturated fatty acids:

· Saturated fatty acids do not contain double bonds,

· while unsaturated fatty acids contain one or more double bonds

Saturated and Unsaturated fatty acids:

· Both saturated and unsaturated fatty acids almost equally occur in the natural lipids

· Fatty acids with one double bond are monounsaturated and those with 2 or more double bonds are collectively known as polyunsaturated fatty acids (PUFA)

Nomenclature of fatty acids:

· Naming of fatty acid is based on hydrocarbon from which it is derived suffix will be –ic acid

· Saturated fatty acid eg: Butyric (butanoic acid): CH₃(CH₂)₂COOH

· Unsaturated fatty acid eg: Oleic acid: CH₃(CH₂)₅CH=CH(CH₂)₇COOH

· In addition to that, fatty acids have some common names

Numbering of carbon atoms:

· It starts from carboxyl carbon which is taken as number 1

· The carbons adjacent to this (carboxyl C) are 2, 3, 4 and so on or alternately a, β, γ and so on

· The terminal carbon containing methyl group is known omega (ω) carbon

· Starting from the methyl end, the carbon atoms in a fatty acid are numbered as omega 1, 2, 3 etc.

· The numbering of carbon atoms in two different ways is given below

Summary