LIPID CHEMISTRY

Dr. Gangadhar Chatterjee

20/9/2012

Objectives:

1. To define LIPIDS. 2. To enumerate the different functions of lipids 3. To give the different classifications of lipids

(FA) according to: Function Simple/Complex Number of carbon atoms Number of double bonds

2

Objectives

4. To understand the nomenclature of FA Family Common name Systematic name Number of C atoms

5. To determine other Lipids and its characteristics

3

LIPIDS

OBESITY Diabetes Mellitus Atherosclerosis

4

Lipids

The fatty substance, separated from salifiable bases, was dissolved in boiling alcohol. On cooling, it was obtained crystallized and very pure, and in this state it was examined. As it has not been hitherto described… I purpose to call it margarine , from Greek word signifying pearl , because one of its characters is to have the appearance of mother of pearl, which it communicates to several of the combinations of which it forms with the salifiable bases. -Michel-Eugene Chevreul, article in Philosophical Magazine, 1814 5

The terminology in this field is rather confusing,variuos other name also suggested as Lipoid, Lipin .But the term LIPID is accepted by biochemists and was suggested by BLOOR. It was also recommened by IUPAC.

Definition:[according to BLOOR]

Compounds having following

charecteristics:

1.Insolubility in water and solubility in fat solvents

2.Some relation to fatty acids as esters ,either actual or potential;

3.Possibility of utilization by living organisms. 6

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 but carbohydrates are the preferable source of energy.

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.

7

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,

8

Roles of Lipids Energy storage (fatty acids, triacylglycerols) Structural elements (phospholipids, cholesterol) Hormones ( sex hormones e.g. Estrogen) Enzyme cofactors (coenzyme A) Electron carriers (coenzyme Q, plastpquinone) Light-absorbing pigments (carotenoids) Hydrophobic anchors (dolichols) Emulsifying agents (bile salts) Intracellular messengers (phosphatidyl inositol)

9

Dietary fat and health

“Mainstream nutritional science has demonized dietary fat, yet 50 years and hundreds of millions of dollars of research have failed to prove that eating a low-fat diet will help you live longer ”

(Science 2001, 291:2536-2545)

10

Nutritional Overview

• Food Sources– Oils, sauces, spreads, butter– Meat, poultry, fish, eggs, nuts (fish oil for omega 3s)– Milk, cheese, dairy– Breads cereals and grains with added fats

• Recommended Intake– Less than or equal to 30% of calories from total fat– Less than or equal to 10% of calories from saturated

fat – No more than 300 mg cholesterol

11

Fats In Food

12

•Milk: (8 oz. serving)• Whole: [3-4 % (legal 3.2%)] 150Kcal• 2%: 120 Kcal• 1%: 100 Kcal• Skim: [<.5%] 90 Kcal

•Cream:• Heavy (Whipping): 36% • Light: 18%• ½ & ½ : 10.5%

•Others:• Mayo: 65% oil, vinegar, sugar, salt, egg yolk• Salad Dressing: 40% oil

Classification of Lipids(mod . From Bloor)

A.Simple Lipids: esters of fatty acid with various alcohols

Neutral Fats and oils: Triglycerides- fatty acid with glycerol

Waxes: esters of FA; higher molecular wt

True waxes

Cholesterol esters

Vitamin A esters

Vitamin D esters

13

Classification of Lipids(mod . From Bloor)

B. Compound Lipids: esters of fatty acids containing in addition to alcohol other groups Phospholipids: phosphoric acid and a

residue Glycolipids residue(Glycosphingolipids) Sulfolipids Lipoproteins Lipopolysaccharides

14

Classification of Lipids(mod . From Bloor)

C.Derived lipids:derivatives obtained by hydrolysis of those given in groups A and B,that still posses general physical characteristics of lipids.

1. Saturated or unsaturated fatty acids

2.Mono or di-glycerides

3. alcohols;

straight chain alcohols

sterols and other steroids, Vit-D

Alcohol having B-ionone ring,Vit-A15

Classification of Lipids(mod . From Bloor)

4.Miscellaneous lipids;

a. Aliphatic Hydrocarbons

b.Carotenoids

c.Squalene

d. vitamin E & K

16

Fatty alcohols

1-Glycerol: It is a trihydric alcohol (i.e., containing

three OH groups) and has the popular name glycerin.

It is synthesized in the body from glucose.

It has the following properties:

17

18

1. Colorless viscous oily liquid with sweet taste.

2. On heating with sulfuric acid or KHSO4 (dehydration) it gives acrolein that has a bad odor. This reaction is used for detection of free glycerol or any compound containing glycerol.

CH 2 OH

CH

CH 2 OH

HO

CHO

CH

CH 2

2 H2O

Heating, KHSO4

Glycerol Acrolein

3-It combines with three molecules of nitric acid to form trinitroglycerin (TNT) that is used as explosive and vasodilator.

4-On esterification with fatty acids it gives: Monoglyceride or monoacyl-glycerol: one

fatty acid + glycerol. Diglyceride or diacyl-glycerol: two fatty

acids + glycerol. Triglyceride or triacyl-glycerol: three fatty

acids + glycerol.

5-It has a nutritive value by conversion into glucose and enters in structure of phospholipids.

19

Uses of Glycerol:

1. Glycerol enters in pharmaceutical and cosmetic preparations.

2. Reduces brain edema in cerebrovascular disease.

3. Nitroglycerin is used as vasodilator especially for the coronary arteries, thus it is used in treatment of angina pectoris. Also, enters in explosives manufacturing.

4. Glycerol is used in treatment of glaucoma (increased intraocular pressure)due to its ability to dehydrate the tissue from its water content.

20

2-Sphingosine:- It is the alcohol(monohydric) present in

sphingolipids. - It is synthesized in the body from serine

and palmitic acid. It is not positive with acrolein test.

21

CH CH NH 2

CH 2OH

CHCH(CH 2)12CH 3

OH

Sphingosine

Fatty AcidsDefinition: Fatty acids are aliphatic mono-carboxylic

acids that are mostly obtained from the hydrolysis of natural fats and oils.

Have the general formula R-(CH2)n-COOH and mostly have straight chain (a few exceptions have branched and heterocyclic chains). In this formula "n" is mostly an even number of carbon atoms (2-34) with a few exceptions that have an odd number.

Fatty acids are classified according to several bases as follows:

22

I. According to presence or absence of double bonds they are classified into:

A-Saturated Fatty Acids they contain no double bonds with 2-24

or more carbons. They are solid at room temperature

except if they are short chained. They may be even or odd numbered. They have the following molecular

formula, CnH2n+1COOH.

23

Saturated fatty acids (no double bond )

A-Short chain Saturated F.A. (2-10 carbon).

a-Short chain Saturated volatile F.A.(2-6 carbon).

b- Short chain Saturated non volatile F.A.(7-10 carbon).

B-Long chain Saturated F.A.(more the10 carbon)

24

a-Volatile short-chain fatty acids: They are liquid in nature and contain

(1-6) carbon atoms. water-soluble and volatile at room

temperature, e.g., acetic, butyric, and caproic acids.

Acetic F.A. (2C ) CH3-COOH.

Butyric F.A. (4C ) CH3-(CH2)2-COOH.

Caproic F.A. (6C ) CH3-(CH2)4-COOH.

25

b-Non-volatile short-chain fatty acids: They are solids at room temperature

and contain 7-10 carbon atoms. They are water-soluble and non-

volatile at room temperature include caprylic and capric F.A.

caprylic (8 C ) CH3-(CH2)6-COOH.

Capric (10 C ) CH3-(CH2)8-COOH.

26

B-Long-chain fatty acids: They contain more than 10 carbon atoms. They occur in hydrogenated oils, animal fats,

butter and coconut and palm oils. They are non-volatile and water-insoluble Include palmitic, stearic, and lignoceric F.A.

palmitic(16C) CH3-(CH2)14-COOH

stearic (18 C ) CH3-(CH2)16-COOH

lignoceric (24C ) CH3-(CH2)22-COOH

27

B-Unsaturated Fatty Acids

They contain double bond monounsaturated

they contain one double bonds .

(CnH2n-1 COOH)

polyunsaturated

they contain more the one double bond (CnH2n-more than 1 COOH).

28

1-Monounsaturated fatty acids:

1-Palmitoleic acid : It is found in all fats. It is C16:1∆9, i.e., has 16 carbons and

one double bond located at carbon number 9 and involving carbon 10.

CH3-( CH2 )5CH = CH-(CH2)7 –COOH

29

2-Oleic acid Is the most common fatty acid in

natural fats. It is C18:1∆9, i.e., has 18 carbons and

one double bond located at carbon number 9 and involving carbon 10.

CH3-(CH2)7- CH=CH – (CH2)7-COOH

30

3-Nervonic acid

(Unsaturated lignoceric acid). It is found in cerebrosides. It is C24:115, i.e., has 24 carbons and

one double bond located at carbon number 15 and involving carbon 16.

CH3 – (CH2)7 CH= CH – (CH2)13- COOH

31

2-Polyunsaturated fatty acids :

(Essential fatty acids): Definition: 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

32

Why they are ESSENTIAL ?

Introduction of additional double bonds in UFAs is limited to the area between COOH group and existing double bond.

So it is not possible to introduce a double bond between –CH3 group at the opposite end (so called w-carbon) and 1st unsaturated linkage.

33

1-Linoleic: C18:29, 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

34

2-Linolenic acid: C18:39, 12, 15, in corn, linseed, peanut, olive,

cottonseed and soybean oils.

CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)7-COOH

35

3-Arachidonic acid: C20:45, 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-CH2-CH=CH-CH2-CH=CH-(CH2)3-COOH

36

Function of Essential Fatty Acids: 1. They are useful in the treatment of atherosclerosis

by help transporting blood cholesterol and lowering it and transporting triglycerides.

2. The hormones are synthesized from them.3. They enter in structure of all cellular and

subcellular membranes and the transporting plasma phospholipids.

4. They are essential for skin integrity, normal growth and reproduction.

5. They have an important role in blood clotting (intrinsic factor).

6. Important in preventing and treating fatty liver.7. Important role in health of the retina and vision.8. They can be oxidized for energy production.

37

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.

38

Docosahexaenoic acid(W3;22:6)

Synthesized from linolenic acid or obtained from fish oil.

Present in high conc. In RETINA, cerebral CORTEX, testes and sperms.

Very important role in vision. Low level reported in Retinitis Pigmentosa.

You can draw the structure39

40

Systematic Nomenclature

According the number of saturated ANOIC

If UNSATURATED ENOIC

41

Important Fatty Acids in Mammalian Tissue (M 411)

Descriptive Name

Systematic Name C Atoms

Double Bonds(DB)

Position of Double Bonds

Unsaturated fatty acid class

1.Acetic2.Lauric3.Myristic4.Palmitic5.Palmitoleic

6.Stearic7.Oleic8.Linoleic9.Linolenic10.Homolinolenic

2.Dodecanoic3.Tetradecanoic4.Hexadecanoic5.Hexadecenoic6.Octadecanoic7.Octadecenoic8.Octadecadenoic9.Octadecatrienoic10. Eicosatrieonic

21214161618181820

000010123

9

99,129, 12,15

W-7

W9W6W3

42

Important Fatty Acids in Mammalian Tissue

Descriptive Name

Systematic Name C Atoms

Double Bonds(DB)

Position of Double Bonds

Unsaturated fatty acid

class

HomolenoleicArachidonic

EPADHA

EicosatrieonicEicosatetraeonicEicosapentaenoicDocosahexaenoic

20202022

3456

8,11,145,8,11,14

5,8,11,14,174,7,10,13,16,

19

W6W6W3w3

43

FA Nomenclature

C atoms are numbered from the CARBOXYL atom ( C 1)

Adjacent to C1 is C2 = α

C3 = β

C4 = γ Methyl end: CH3 is known as ω or the

44

FA Nomenclature

Δ indicates the number and position of the double bond :ex Δ9 indicates a double bond between 9-10

ω 9 indicates a double bond on the ninth C based on the ω terminal

45

OLEIC ACID

46

Oleic Acids

18:1:9 Δ9 18:1 18 10 9 1 CH3(CH2)7CH10=CH(CH2)7COOH

ωC18:1 or n-9,18:1 ω 2 3 4 5 6 7 8 9 10 18

CH3CH2CH2CH2CH2CH2CH2CH2CH2=CH(CH2)7COOH

47

Unsaturated FA

GEOMETRIC ISOMERISM Occurs depending on the orientation of

atoms around the axes of the double bond If the ACYLchain are on the same side of the

bond it is CIS If it is on the opposite TRANS Almost all naturally occurring UFA= CIS

48

There is free rotation about C-C bonds in the fatty acid hydrocarbon, except where there is a double bond.

Each cis double bond causes a kink in the chain.

Rotation about other C-C bonds would permit a more linear structure than shown, but there would be a kink.

C

O

O 1

23

4

fatty acid with a cis-9 double bond

49

Fatty acids in food: saturated vs unsaturated

Source Lauric/Myristic Palmitic Stearic Oleic Linoleic

Beef 5 26-32 20-25 37-43 2-3 Milk 25 12 33 3Coconut 74 10 2 7Corn 8-12 3-4 19-24 34-62Olive 9 2 84 4Palm 39 4 40 8Soybean 9 6 20 52Sunflower 6 1 21 66

50

Fatty acid composition of three food fats

51

Fats and Oils

52

Blockages are serious because they can result in a heart attack or stroke. Arteries also lose their elasticity when fats accumulate on the walls and absorb calcium. This leads to a condition called arteriosclerosis or hardening of the arteries. High blood pressure is a symptom of arteriosclerosis. You need to know this because we don’t want our family members to die young.

You probably didn’t realize it but the Omega-3 present in fish oil reduces the aggregation of blood platelets, inhibits the formation of thrombi, reduces blood triglyceride levels, and has a vasodilatory effect on blood vessels. Omega-3 is important in the normal immune response, and suppresses the production of inflammation Omega-3 are even required for the normal development and function of the brain; a deficiency in omega-3 results in impaired learning difficulty.

Fish oils are polyunsaturated fats that are healthy especially if they include omega 3That’s animal fat that is healthy and that’s why anchovies on my pizza make it healthier.

Take a look at these clogged arteries. Arteries normally must be elastic to expand with the heart systolic pressure.

53

Trans fats are are solid fats created by artificially adding hydrogen into cooking oils. Partially hydrogenated vegetable oils are used for frying French fries and chicken and for baking croissants, cookies, and donuts. Trans fats add shelf life to products and make oils last longer in deep fryers. Chances are that if you eat fast food you are getting a good dose of trans fat.

Notice the trans fat molecule has hydrogens across from one another forming a straight line molecule. The healthy cis fat has the hydrogens on the same side and forms a bent molecule

IS ZERO REALLY ZERO?If a food has exactly 0.49 grams of trans fat per serving, it will say “Trans Fat: 0 grams” on the label.

54

55

Possible risks related to trans fatty acids

Major trans FA found in food: 18:1t (less amount of 16:1t and 18:2t)

Sources of tFA: margarine, cakes, cookies, chips etc.

Link tFA to breast cancer (http://www.sciencedaily.com)

Link tFA to increased serum cholesterol (http://cardiology.medscape.com http://nutrition.about.com)

56

1-Simple LipidsA-Neutral Fats and oils (Triglycerides)Definition:• - They are called neutral because they are

uncharged due to absence of ionizable groups in it.

• The neutral fats are the most abundant lipids in nature. They constitute about 98% of the lipids of adipose tissue, 30% of plasma or liver lipids, less than 10% of erythrocyte lipids.

57

Adipocyte

58

• They are esters of glycerol with various fatty acids. Since the 3 hydroxyl groups of glycerol are esterified, the neutral fats are also called “Triglycerides”.

• Esterification of glycerol with one molecule of fatty acid gives monoglyceride, and that with 2 molecules gives diglyceride.

H2C O

C HO

H2C

C

C

O C

R1

R3

R2

O

O

O

+

3 H2O

CH 2 OH

C HHO

CH 2 OH

HO C R1

O

HO C R3

O

HO C R2

O

Fatty acids Glycerol Triglycerides(Triacylglycerol)

59

Types of triglycerides1-Simple triglycerides: If the three fatty acids

connected to glycerol are of the same type the triglyceride is called simple triglyceride, e.g., tripalmitin.

2-Mixed triglycerides: if they are of different types, it is called mixed triglycerides, e.g., stearo-diolein and palmito-oleo-stearin.

• Natural fats are mixtures of mixed triglycerides with a small amount of simple triglycerides.

60

CH 2 O

C HO

CH 2

C

C

O C

(CH 2)14

O

O

O

Tripalmitin(simple triacylglycerol)

CH 3

(CH 2)14CH 3

(CH 2)14 CH 3

CH 2 O

C HO

CH 2

C

C

O C

(CH 2)16

O

O

O

1-Stearo-2,3-diolein(mixed triacylglycerol)

CH 3

(CH 2)7CHCH(CH 2)7CH 3

(CH 2)7 CH CH (CH 2)7 CH 3

CH 2 O

C HO

CH 2

C

C

O C

(CH 2)14

O

O

O

1-palmito-2-oleo-3-stearin(mixed triacylglycerol)

CH 3

(CH 2)16 CH 3

(CH 2)7CHCH(CH 2)7CH 3

61

• The commonest fatty acids in animal fats are palmitic, stearic and oleic acids.

• The main difference between fats and oils is for oils being liquid at room temperature, whereas, fats are solids.

• This is mainly due to presence of larger percentage of unsaturated fatty acids in oils than fats that has mostly saturated fatty acids.

62

Physical properties of fat and oils:1. Freshly prepared fats and oils are colorless,

odorless and tasteless.Any color, or taste is due to association with other foreign substances, e.g., the yellow color of body fat or milk fat is due to carotene pigments(cow milk).

2. Fats have specific gravity less than 1 and, therefore, they float on water.

3. Fats are insoluble in water, but soluble in organic solvents as ether and benzene.

4. Melting points of fats are usually low.

63

Melting Points and Solubility in Water of Fatty Acids

S olu b ilit y in H O

Ch ain Len g t h

2

Melt in g Poin t

64

Van der Waals interactions between the acyl chains: ↑ cis double bonds Tm

65

Effects of Double Bonds on the Melting Points

16:0 

6016:1 118:0 6318:1 1618:2 -518:3 -1120:0 75

F. A. M. P. (0C)

20:4 -50 

M.P.

# Dou b le b on d s 66

Chemical Properties of fats and oils:1-Hydrolysis:• They are hydrolyzed into their constituents (fatty acids and

glycerol) by the action of super heated steam, acid, alkali or enzyme (e.g., lipase of pancreas).

• - During their enzymatic and acid hydrolysis glycerol and free fatty acids are produced.

CH 2 O

C HO

CH 2

C

C

O C

R1

R3

R2

O

O

O

3 H2O

H2C OH

C HHO

H2C OH

OHCR1

O

OHCR3

O

+ OHCR2

OLipase or Acid

Triacylglycerol Glycerol Free fatty acids67

2-Saponification. Alkaline hydrolysis produces glycerol and salts of fatty acids (soaps).

• Soaps cause emulsification of oily material this help easy washing of the fatty materials

CH 2 O

C HO

CH 2

C

C

O C

R1

R3

R2

O

O

OH2C OH

C HHO

H2C OH

ON aCR1

O

ON aCR3

O

+ ON aCR2

O

Triacylglycerol Glycerol Sodium salts of fatty acids (soap)

3 NaOH

68

Soap:

Long Chain Fatty Acid Salt

Soap:

Long Chain Fatty Acid Salt

Fatty acid

Na+CO

O-

Nonpolar Polar

FatFat with soap is water soluble 69

3-Halogenation• Neutral fats containing unsaturated fatty acids have the

ability of adding halogens (e.g., hydrogen or hydrogenation and iodine or iodination) at the double bonds.

• - It is a very important property to determine the degree of unsaturation of the fat or oil that determines its biological value

CH (CH 2)7 COO HCHCH 2CH

Linoleic acidCH(CH 2)4CH 3

2 I2

CH (CH 2)7 COO HCHCH 2CH

Stearate-tetra-iodinate

CH(CH 2)4CH 3

II I I

70

4.Hydrogenation of Oils

71

• It is a type of addition reactions accepting hydrogen

at the double bonds of unsaturated fatty acids.• The hydrogenation is done under high pressure of

hydrogen and is catalyzed by finely divided nickel or copper and heat.

• It is the base of hardening of oils (margarine manufacturing), e.g., change of oleic acid of fats (liquid) into stearic acid (solid).

• It is advisable not to saturate all double bonds; otherwise margarine produced will be very hard, of very low biological value and difficult to digest.

72

Oils(liquid)

(with unsaturated fatty acids, e.g., oleic)

Hard fat(margarine, solid)(with saturated

fatty acids, e.g., stearic)

Hydrogen, high pressure, nickel

Advantages for hydrogenated oil or fat are as follows:1. It is more pleasant as cooking fat.2. It is digestible and utilizable as normal animal fats and oils.3. It is less liable to cause gastric or intestinal irritation.4. It is easily stored and transported and less liable to

rancidity. Disadvantages of hydrogenated • fats include lack of fat-soluble vitamins (A, D, E and K) and

essential fatty acids

73

5-Oxidation• 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

74

RancidityDefinition:• 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.

75

Types and causes of Rancidity:1. Hydrolytic rancidity2. Oxidative rancidity3. Ketonic rancidity1-Hydrolytic rancidity:• It results from slight hydrolysis of the fat by lipase

from bacterial contamination leading to the liberation of free fatty acids and glycerol at high temperature and moisture.

• Volatile short-chain fatty acids have unpleasant odor.

76

CH 2 O

C HO

CH 2

C

C

O C

R1

R3

R2

O

O

O

3 H2O

H2C OH

C HHO

H2C OH

OHCR1

O

OHCR3

O

+ OHCR2

OLipase

Triacylglycerol Glycerol Free fatty acids(volatile, bad odor)

77

2-Oxidative Rancidity: • It is oxidation of fat or oil catalyzed by

exposure to oxygen, light and/or heat producing peroxide derivatives which on decomposition give substances, e.g., peroxides, aldehydes, ketones and dicarboxylic acids that are toxic and have bad odor.

• This occurs due to oxidative addition of oxygen at the unsaturated double bond of unsaturated fatty acid of oils.

78

Polyunsaturated fatty acid

Peroxyradical

Oxidant, O2

Hydroperoxide

Hydroxy fatty acid

Cyclic peroxide

Aldehydessuch as malondialdehyde

Other fragmentssuch as dicarboxylic acids

79

3-Ketonic Rancidity: • It is due to the contamination with certain

fungi such as Asperigillus Niger on fats such as coconut oil.

• Ketones, fatty aldehydes, short chain fatty acids and fatty alcohols are formed.

• Moisture accelerates ketonic rancidity.

80

• Prevention of rancidity is achieved by:1. Avoidance of the causes (exposure to light, oxygen,

moisture, high temperature and bacteria or fungal contamination). By keeping fats or oils in well-closed containers in cold, dark and dry place (i.e., good storage conditions).

2. Removal of catalysts such as lead and copper that catalyze rancidity.

3. Addition of anti-oxidants to prevent peroxidation in fat (i.e., rancidity). They include phenols, naphthols, tannins and hydroquinones. The most common natural antioxidant is vitamin E that is important in vitro and in vivo.

81

Hazards of Rancid Fats:1. The products of rancidity are toxic, i.e.,

causes food poisoning and cancer.2. Rancidity destroys the fat-soluble vitamins

(vitamins A, D, K and E).3. Rancidity destroys the polyunsaturated

essential fatty acids.4. Rancidity causes economical loss because

rancid fat is inedible.

82

Analysis and Identification of fats and oils(Fat Constants)

• Fat constants or numbers are tests used for:1. Checking the purity of fat for detection of

adulteration.2. To quantitatively estimate certain properties of fat.3. To identify the biological value and natural

characteristics of fat.4. Detection of fat rancidity and presence of toxic

hydroxy fatty acids.

83

1-Iodine number (or 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, as a natural property for it. • Unsaturated fatty acids absorb iodine at their

double bonds, therefore, as the degree of unsaturation increases iodine number 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.

• For olive oil more than 88 suggest adulteration.

84

2-Saponification number (or value):• Definition: It is the number of milligrams of KOH

required to completely saponify one gram of fat.• 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.

85

3-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.

86

4-Reichert- Meissl Number (or value):• Definition: It is the number of milliliters of 0.1 N

KOH required to neutralize the 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.

87

5-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.

88

B-Waxes• Definition: Waxes are solid simple lipids containing

a monohydric alcohol (with a higher molecular weight than glycerol) esterified to long-chain fatty acids. Examples of these alcohols are palmitoyl alcohol, cholesterol, vitamin A or D.

• Properties of waxes: Waxes are insoluble in water, but soluble in fat solvents and are negative for acrolein test.

• Waxes are not easily hydrolyzed as the fats and are indigestible by lipases and are very resistant to rancidity.

• Thus they are of no nutritional value.

89

Type of Waxes:• - Waxes are widely distributed in nature such as the

secretion of certain insects as bees-wax, protective coatings of the skins and furs of animals and leaves and fruits of plants. They are classified into true-waxes and wax-like compounds as follows:

A-True waxes: include:• Bees-wax is secreted by the honeybees that use it to

form the combs. It is a mixture of waxes with the chief constituent is mericyl palmitate.

90

91

Waxes

C15H31 C OHO

+C30H61OH C15H31 C OO

C30H61

H2OPalmiticacid

Mericylalcohol

Mericylpalmitate

B-Wax-like compounds: • Cholesterol esters: Lanolin (or wool fat) is

prepared from the wool-associated skin glands and is secreted by sebaceous glands of the skin.

• It is very complex mixture, contains both free and esterified cholesterol, e.g., cholesterol-palmitate and other sterols.

92

Differences between neutral lipids and waxes:

Waxes Neutral lipids

1.Digestibility: Indigestible (not hydrolyzed by lipase).

Digestible (hydrolyzed by lipase).

2-Type of alcohol:

Long-chain monohydric alcohol + one fatty acid.

Glycerol (trihydric) + 3 fatty acids

3-Type of fatty acids:

Fatty acid mainly palmitic or stearic acid.

Long and short chain fatty acids.

4-Acrolein test: Negative. Positive.

5-Rancidability: Never get rancid. Rancidible.

6-Nature at room temperature.

Hard solid. Soft solid or liquid.

7-Saponification Nonsaponifiable. Saponifiable.

8-Nutritive value:

No nutritive value. Nutritive.

9-Example: Bee & carnuba waxes. Butter and vegetable oils.93

METHODS TO IDENTIFY LIPIDS

OLDER METHODS

Based on classic chemical procedures: crystallization, distillation, solvent extraction

NEWER METHODS Chromatography

1. Thin-layer chromatography – for separation of various lipid classes

2. Gas-liquid chromatography – separation of individual fatty acids

Extraction is done using chloroform and methanol

94

Testing for lipids•Grease spot test/Brown paper test•Sudan Red test

95

Brown paper test for lipids

As we all know from

experience, lipids leave translucent

spots (grease spots) on

unglazed brown paper bags.

96

Sudan Red test for lipids

Sudan red is a fat-soluble dye

that stains lipids red. Using

Sudan red can show the

amount and the location of

lipids.97

Fat Substitutes[Artificial fats]

Simplex– Egg white and milk protein– very small 0.1 – 0.3uM – microencapsulated

Oatrium – from oat bran or flourAvicel – microcrystalline cellulose (from

wood) (0 calories)

98

Artificial fats (fat substitutes )

Olestra: - an artificial fat created from sucrose (replace of glycerol) and up to eight fatty acids;

- too large to be metabolized and passes through the body unchanged, but because it acts as a lipid, it can cause depletion of fat-soluble vitamins.

99

100

Books that made LIPID healthier;

Text book of Biochemistry-Chatterjea, Shinde

Biochemistry illustrated-Harper Biochemistry-Orten Principals of Biochemistry-Lehninger Medical Biochemistry-N.V.Bhagaban

101

THANK YOU

102