Dilla University College of Health Science

Department of Pharmacy

Chemistry of Natural Product(phar2081)

(Lipids)
Hailemikael G/Mariam (Msc)
Dilla, Ethiopia
© 2024
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Topics to be discussed

• Definition

• Occurrence and composition of fats, oils and waxes;

• Classifications of lipids

• Reactions of fats and oils

• Determination of analytical values for fats and oils

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Introduction
Definition:

• Lipids are organic compounds formed mainly from alcohol and fatty acids
combined together by ester linkage.

• Any of a class of organic compounds that are fatty acids or their derivatives and

are insoluble in water but soluble in organic solvents

O
H2O O
R CH2 OH R CH2 O
+ HO C R C R
Fatty alcohol Fatty acid Esterase (lipase) ester (lipid)

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Introduction
• Lipids are the polymers of fatty acids that contain a long, non-polar
hydrocarbon chain with a small polar region containing oxygen. The
lipid structure is explained in the diagram below

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Introduction
• A fatty acid is

• A molecule characterized by the presence of a carboxyl group attached to a long

hydrocarbon chain.

• A molecule with a formula R–COOH where R is a hydrocarbon chain

• Fatty acids can be said to be carboxylic acids

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Introduction
• Properties of Lipids
• Lipids are insoluble in water, but soluble in fat or organic solvents (ether, chloroform,
benzene ).

• Lipids include fats, oils, waxes and related compounds.

• They are widely distributed in nature both in plants and in animals.

• Lipids are oily or greasy nonpolar molecules, stored in the adipose tissue of the body.

• Lipids are a heterogeneous group of compounds, mainly composed of hydrocarbon chains

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Introduction
Biological Importance of Lipids:
1. They are more palatable and storable to unlimited amount compared to carbohydrates.
2. They have a high-energy value (25% of body needs) and they provide more energy per
gram than carbohydrates and proteins
3. Supply the essential fatty acids that cannot be synthesized by the body.
4. Supply the body with fat-soluble vitamins (A, D, E and K).
5. They are important constituents of the nervous system.
6. Tissue fat is an essential constituent of cell membrane and nervous system. It is mainly
phospholipids in nature that are not affected by starvation.

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Introduction
7-Stored lipids “depot fat” is stored in all human cells acts as:
A store of energy.
A pad for the internal organs to protect them from outside shocks.
A subcutaneous thermal insulator against loss of body heat.
8-Lipoproteins, which are complex of lipids and proteins, are important cellular constituents
that present both in the cellular and subcellular membranes.
9-Cholesterol enters in membrane structure and is used for synthesis of adrenal cortical
hormones, vitamin D3 and bile acids.
10- Lipids provide bases for dealing with diseases such as obesity, atherosclerosis, lipid-
storage diseases, essential fatty acid deficiency, respiratory distress syndrome,

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Classification of Lipids
• Lipids can be classified into two main classes

a) Nonsaponifiable lipids

b) Saponifiable lipids

a) Nonsaponifiable Lipids

• A nonsaponifiable lipid cannot be disintegrated into smaller molecules through

hydrolysis with acid/base/enzyem. These include steroids, prostaglandins, etc

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Classification of Lipids
b) Saponifiable Lipids
• Saponifiable lipid comprises one or more ester groups,
• It to undergo hydrolysis in the presence of a base, acid, or enzymes, including waxes,
triglycerides, sphingolipids and phospholipids.
• Further, these categories can be divided into non-polar and polar lipids.
• Nonpolar lipids, namely triglycerides, are utilized as fuel and to store energy.
• Polar lipids, that could form a barrier with an external water environment, are utilized in
membranes.
• Polar lipids comprise sphingolipids and glycerophospholipids.

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Classification of Lipids

Based on structure

1. Simple lipids

2. Compound or conjugated lipids

3. Derived Lipids

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Classification of Lipids
• Simple Lipids :Esters of fatty acids with various alcohols.
• Fats: Esters of fatty acids with glycerol. Oils are fats in the liquid state
• Waxes: Esters of fatty acids with higher molecular weight monohydric
alcohols
• Compound Lipids Esters of fatty acids containing groups in addition to alcohol
and a fatty acid.
• Phospholipids: These are lipids containing, in addition to fatty acids and
alcohol, a phosphoric acid residue.
• They frequently have nitrogen-containing bases and other substituents, eg, in
glycerophospholipids the alcohol is glycerol and in sphingophospholipids the
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Classification of Lipids
• Glycolipids (glycosphingolipids): Lipids containing a fatty acid, sphingosine
and carbohydrate.
• Other complex lipids: Lipids such as sulfolipids and amino lipids.
Lipoproteins may also be placed in this category.

Derived lipids
include fatty acids and alcohols,

are the building blocks for the simple and complex lipids

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Classification of Lipids
Waxes
• Waxes are “esters” (an organic compound made by replacing the hydrogen with
acid by an alkyl or another organic group) formed from long-alcohols and long-
chain carboxylic acids.

• Waxes are found almost everywhere. Fruits and leaves of many plants possess
waxy coatings, that can safeguard them from small predators and dehydration.

• Fur of a few animals and the feathers of birds possess same coatings serving as
water repellants.
• Carnauba wax is known for its water resistance and toughness (significant for car
wax).

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Fixed oils and fats
• Fixed oils and fats are obtained from plants or animal.
• They are rich in calories and in plant source, they are present mostly in the seeds,
as reserve substances and in animals .
• They differ only according to their melting point and chemically they belong to
the same group.
• If a substance is liquid at 15.5–16.5°C it is called fixed oil and solid or semisolid
at the above temperature, it is called fat.
• They are made from two kinds of molecules: glycerol (a type of alcohol with a
hydroxyl group on each of its three carbons) and three fatty acids joined by
dehydration synthesis.

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Fixed oils and fats
• Since there are three fatty acids attached, these are known as triglycerides. These
fatty acids may be saturated, monounsaturated or polyunsaturated..
• The terms saturated, mono-unsaturated, and poly-unsaturated refer to the number
of hydrogens attached to the hydrocarbon tails of the fatty acids as compared to
the number of double bonds between carbon atoms in the tail.
• Fats, which are mostly from animal sources, have all single bonds between the
carbons in their fatty acid tails, thus all the carbons are also bonded to the
maximum number of hydrogens possible.
• Since the fatty acids in these triglycerides contain the maximum possible amount
of hydrogens, these would be called saturated fats

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Classifications of lip..
According to biosynthesis in the body
• Essential Fatty acids – those that cannot be biosynthesized in the body
examples: linoleic and linolenic acids

• Non-essential Fatty acids - can be biosynthesized in the body

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Essential fatty acids
• They are essential fatty acids that can not be synthesized in the human body and
must be taken in adequate amounts in the diet.
• They are required for normal growth and metabolism
• Source: vegetable oils such as corn oil, linseed oil, peanut oil, olive oil, cottonseed
oil, soybean oil and many other plant oils, cod liver oil and animal fats.
• Deficiency: Their deficiency in the diet leads to nutrition deficiency disease.
• Its symptoms include: poor growth and health with susceptibility to infections,
dermatitis, decreased capacity to reproduce, impaired transport of lipids, fatty
liver, and lowered resistance to stress.

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Essential fatty acids
1-Linoleic:
• C18:29, 12
• It is the most important since other essential fatty acids can be synthesized from it in the body.
CH3-(CH2)4-CH = CH-CH2-CH=CH-(CH2)7-COOH
2-Linolenic acid:
• C18:39, 12, 15
• in corn, linseed, peanut, olive, cottonseed and soybean oils.
• CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)7-COOH
3-Arachidonic acid:
• C20:45, 8, 11, 14
• It is an important component of phospholipids in animal and in peanut oil from which prostaglandins
are synthesized.
CH3-(CH2)4-CH=CH-CH2-CH=CH-CH -CH=CH-CH2-CH=CH-(CH2)3-COOH
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 Examples of fatty acids

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 Chemical reactions of fatty acids

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 Chemical reactions of fatty acids
2. Formation of Halides

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Chemical reactions of fatty acids
3. Hydrolysis

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 4. Saponification

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Chemical reactions of fatty acids
5. Hydrogenation

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Chemical reactions of fatty acids
• 6-Oxidation(Rancidty)

• This toxic reaction of triglycerides leads to unpleasant odour or taste of oils and
fats developing after oxidation by oxygen of air, bacteria, or moisture.

• Also this is the base of the drying oils after exposure to atmospheric oxygen.

Example is linseed oil, which is used in paints and varnishes manufacturing

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Chemical reactions of fatty acids
Definition:

• It is a physico - chemical change in the natural properties of the fat leading to the
development of unpleasant odor or taste or abnormal color particularly on aging
after exposure to atmospheric oxygen, light, moisture, bacterial or fungal
contamination and/or heat.

• Saturated fats resist rancidity more than unsaturated fats that have unsaturated
double bonds.

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Analytical parameters to determine the value of fats and oils

 The properties of oils and fats vary along with the degree of unsaturation,
average molecular weight and also acidity from hydrolysis.
 Fat oil constants or numbers are tests used for:
1.To check the purity of fat for detection of adulteration.
2.Quantitative estimate certain properties of fat.
3.To identify the biological and natural characteristics of fat.
4.To detect rancidity and presence of toxic hydroxy fatty acids.

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Analytical parameters to determine the value of fats and oils

 A number of parameters are used for their analysis which are included
under

physical constants and

Chemical constants.

 Physical constants include viscosity, specific gravity, refractive index,

solidification point etc.

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Physical constants/tests
Specific gravity:
The ratio of the mass of a substance to the mass of an equal volume of another
substance taken as standard

sp. gr. = Ws/Ww Ws=wt of substance

• Ww=wt of water
sp. gr. at 25°c
Palm oil 0.898-0.901
Mustard oil 0.914-0.920
Corn oil 0.914-0.921

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Physical constants/tests
ii. Refractive index

• When a ray of light passes from one medium to another of different density, it is
bent from original path.

• Thus the ratio of the velocity of light in vacuum to its velocity in the substance is
termed as refractive index of the second medium

• Depending upon the purity it is constant for a liquid and can be considered as one
of the criteria for its standardization

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Physical constants/tests
• Refractive index of a cpd varies with wave length of the incident light,
temperature, and pressure
• Fats have definite angles of refraction.
• Variation from the normal value indicates adulteration of fats or oils.
• Refractive indices of following cpds are for Na light and at 25°c
Arachis oil 1.4678 to 1.470
Caster oil 1.4758 to 1.527
Sunflower 1.466 to 1.468

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Physical constants/tests

iii. Melting point

• it is one of the parameters to judge the purity of chemicals and phytochemicals.
• MPs of pure cpds are very sharp and constant
• MPs of some saturated FAs
MP
 Capric acid C9H19COOH 31.3
 Palmitic C15H31COOH 63.0
 Stearic C17H35COOH 69.6

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Physical constants/tests

iv. Viscosity
• Is resistance in flow of liquid
• Viscosity of a liquid is constant at a given temp. and it is an index of its
composition
• Hence it can used as a means of standardising liquid drugs
Eg.
 Liquid paraffin – kinematic viscosity is 64 centistole at 37°c
 Pyroxylin – kinematic viscosity 1100-2450 centistole

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Chemical constants
1-Total fat
• Definition: Total fat is a total amount of saturated and unsaturated fat in crude material

• It can be determined by extraction with ether

A weighed amount of the material is treated with a small amount of ether in an

extractor &

When the extraction is complete, the ether solution is with drawn & then evaporated
to leave the residue of fat

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Chemical constants
2, Iodine value
• Definition: It is the number of grams of iodine absorbed by 100 grams of fat or oil.
• Uses: It is a measure for the degree of unsaturation of the fat
• Unsaturated fatty acids absorb iodine at their double bonds, therefore, as the
degree of unsaturation increases iodine number increase and hence biological
value of the fat increase.
• It is used for identification of the type of fat, detection of adulteration and
determining the biological value of fat.
Non-drying oils <100 (eg. Olive oil: 79-88)
Semi-drying oils 100-130 (eg. Cottonseed oil: 103-111)
Drying oils >130 (eg. Linseed oil: 175-202)

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Chemical constants
• Significance:

• Iodine value is the measure of unsaturation ( number of double bond ) in fat.

• Iodine number is useful to analyze the degree of adulteration

• On basis of iodine value the oils can be differentiated into non-drying oil and
semidrying oil.

• Drying oil shows less iodine value, non-drying oil

• shows more iodine value and semidrying oil shows moderate iodine value.

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chemical constants
3-Saponification number (or value):
• Definition: It is the number of milligrams of KOH required to completely saponify fatty
acids in one gram of fat.
• It can be determined by refluxing a known amount of the sample with excess of standard
alcoholic KOH solution, and then titrating the unused alkali against a standard acid
solution
• It gives a clue about the molecular weight and size of the fatty acid in the fat or oil.
• Uses: Since each carboxyl group of a fatty acid reacts with one mole of KOH during
saponification, therefore, the amount of alkali needed to saponify certain weight of fat
depends upon the number of fatty acids present per weight.
• Thus, fats containing short-chain acids will have more carboxyl groups per gram than
long chain fatty acids and consume more alkali, i.e., will have higher saponification
number.
Butter (large proportion of short chain Fas): 220-230
Oleomargarine (long chain Fas): ≤195

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Chemical constants
4-Acids Number (or value):
• Definition: It is the number of milligrams of KOH required to neutralize the free
fatty acids present in one gram of fat.
• Uses: It is used for detection of hydrolytic rancidity because it measures the
amount of free fatty acids present.
• It can be determined by dissolving a weight amount of the fat in alcohol and
titrating the solution against standard alkali solution using phenolphthalein as an
indicator a high acid value would be expected in a rancid fat

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Chemical constants
5-Reichert- Meissl Number:
• Definition: It is the number of milliliters of 0.1 N KOH required to neutralize the
volatile water-soluble fatty acids distilled from 5 grams of fat. Short-chain fatty
acid (less than 10 carbons) is distillated by steam.
• Uses: This studies the natural composition of the fat and is used for detection of
fat adulteration.
• Butter that has high percentage of short-chain fatty acids has highest Reichert-
Meissl number compared to margarine.
Butter fat RMV = 17-34
Cattonseed oil <1

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Chemical constants

3, Acid value
• Acid value is defined as the number of milligrams of potassium hydroxide
required to neutralize the free fatty acids present in 1gm of sample of fat or oil.
• Significance:
Acid value is used as an indication of rancid state.
Generally rancidity causes free fatty acids, which have been liberated by hydrolysis
of glycerides due to the action of moisture, temperature or enzyme lipase.

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Chemical constants
4, Acetyl Number (or value):
• Definition: It is number of milligrams of KOH needed to neutralize the acetic
acid liberated from hydrolysis of 1 gram of acetylated fat (hydroxy fat reacted
with acetic anhydride).
• Uses: The natural or rancid fat that contains fatty acids with free hydroxyl groups
are converted into acetylated fat by reaction with acetic anhydride.
• Thus, acetyl number is a measure of number of hydroxyl groups present.
• It is used for studying the natural properties of the fat and to detect adulteration
and rancidity.

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Chemical constants
5, polenski number
• Definition: It is the number of millilitres of 0.1N potassium hydroxide solution
required to neutralize the water-insoluble, steam distillable acid librated by
hydrolysis of five gms of fat

• It is measure of the steam-distillable, water insoluble acid constituents of the fat

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chemical constants
6-unsaponifiable matter

• Definition: Unsaponifiable matter is part of the fat or oil which is insoluble in water or
incapable of forming a soluble soap with alkalis

• Pure edible fats and oils generally contain 1 to 2% of unsaponifiable matter

• For extraction of unsaponifiable matter, the given fat is saponified and then warm water is
added it when the unsaponifiable matter appears as oily drops or as a milkiness, which is
then separated by extraction with petroleum ether e.g. Sterols & certain vitamins

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Chemical constants
7-Ester value

• It is defined as number of milligrams of potassium hydroxide required to

combine with fatty acids which are present in glyceride form in 1 g sample of oil
or fat.

•Difference between saponification value and acid value is ester value.

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