Chapter 3-Chemmmmmmmmmistry of Lipids.ppt

c n

2. Lipids are organic compounds formed mainly from
alcohol and fatty acids combined together by ester
linkage
2
CH
2
R
Fatty alcohol
OH C R
Fatty acid
HO
O
+
H
2O
CH
2
R OC R
O
Esterase (lipase)
ester (lipid)

3. 3
Generally, lipids
 Are chemically heterogeneous group of substances,
Having in common the property of insolubility in water, but
solubility in non-polar solvents
 May include natural products such as fatty acids and
their derivatives, steroids, terpenes, carotenoids and
bile acids

4. Lipids are insoluble in water, but soluble in fat or
organic solvents (ether, chloroform, benzene,
acetone)
Lipids also include fats, oils, waxes and related
compounds
They are widely distributed in nature both in
plants and in animals
4

5. Biological Importance of Lipids:
1.They are more palatable and storable
2.They provide more energy per gram than (25% of body
needs) carbohydrates and proteins but carbohydrates are
the preferable source of energy
3.Supply the essential fatty acids
4.Supply 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
7.A pad for the internal organs to protect them from outside
shocks
8.Precursors of hormones (steroids and prostaglandins)
5

6. Different basis of classifications:
1. Physical properties at room temperature
Oils are liquid and
Fats are solid or semisolid
2.Polarity (polar and neutral lipids)
 Neutral (non-polar) lipids include fatty acids, alcohols,
glycerides, and sterols
 Polar lipids include glycerophospholipids and
glyceroglycolipids
3.Essentiality for humans
Essential and
Nonessential fatty acids
6

7. 4. Structure (simple or complex)
The separation into polarity classes is rather arbitrary, as some
short chain fatty acids are very polar
A classification based on structure is, therefore, preferable.
Based on structure, lipids can be classified as derived, simple,
or complex
Derived lipids
Include fatty acids and alcohols.
Are the building blocks for the simple and complex lipids
 Simple lipids
Composed of fatty acids and alcohol components,
Include acylglycerols, ether acylglycerols, sterols, and their
esters and wax esters
7

8. In general terms, simple lipids can be hydrolyzed to two
different components, usually an alcohol and an acid
Complex lipids
Include glycerophospholipids (phospholipids),
glyceroglycolipids (glycolipids), and sphingolipids
These structures yield three or more different compounds
on hydrolysis
8

9. A. Fatty alcoholsA. Fatty alcohols
1. 1. Glycerol:Glycerol:
It is a trihydric alcohol (i.e., containing three OH
groups) and has the popular name glycerin
 It has the following properties:
1. Colorless viscous oily liquid with sweet taste
2. On heating with sulfuric acid or KHSO
4 (dehydration) it
gives acrolein that has a bad odor
This reaction is used for detection of free glycerol or any
compound containing glycerol
9

10. 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
10
CH
2
OH
CH
CH
2
OH
HO
CHO
CH
CH
2
2 H
2O
Heating, KHSO
4
Glycerol Acrolein

11. Uses of Glycerol :Uses of Glycerol :
1.Glycerol enters in pharmaceutical and cosmetic
preparations
2.Reduces brain edema in cerebrovascular disease via
improving blood flow
3.Nitroglycerin is used as vasodilator especially for the
coronary arteries, thus it is used in treatment of angina
pectoris and 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
11

12. 22. Sphingosine:
- It is the alcohol(dihydric) present in sphingolipids
- It is synthesized in the body from serine and palmitic
acid
It is not positive with acrolein test
12
CHCHNH
2
CH
2
OH
CHCH(CH
2
)
12
CH
3
OH
Sphingosine

13. Fatty acids are aliphatic mono-carboxylic acids
 Mostly obtained from the hydrolysis of natural fats
and oils
Have the general formula R-(CH
2)
n-COOH
In this formula "n" is mostly an even number of
carbon atoms (2-34) with a few exceptions that have
an odd number
Mostly have straight chain
13

14. Fatty acids are classified according to several bases as follows:
According to presence of double bond(s)
Saturated – no double bond
Unsaturated – one or more double bond
According to chain length
Short chain FAs: 2-4 carbon atoms
Medium chain FAs: 6 –10 carbon atoms
Long chain FAs: 12 – 26 or more carbon atoms
According to biosynthesis in the body:
Non-essential FAs - can be biosynthesized in the body(stearic, oleic and
palmitic acid)
Essential FAs – those that cannot be biosynthesized in the body
Examples: linoleic and linolenic acids----Omega-6 FA
14

15. 15
A-Saturated Fatty Acids

Contain no double bonds with 2-24 or more carbons

Solid at room temperature except if they are short
chained

May be even or odd numbered
Have the molecular formula, C
nH
2n+1COOH

16. Saturated fatty acidsSaturated fatty acids
A-Short chain Saturated F.A. A-Short chain Saturated F.A. (2-10 carbon).(2-10 carbon).
1.Short chain Saturated volatile F.A.(2-6 carbon)
2.Short chain Saturated non volatile F.A.(7-10 carbon)
B-Long chain Saturated F.AB-Long chain Saturated F.A.(more the10 carbon).(more the10 carbon)
16

17. A. Short chain Saturated F.A.A. Short chain Saturated F.A.
a-Volatile short-chain fatty acids:
 They are liquid in nature and contain (They are liquid in nature and contain (2-6)2-6) carbon carbon
atomsatoms
 water-soluble and volatile at room temperature, e.g., water-soluble and volatile at room temperature, e.g.,
acetic, butyric, and caproic acidsacetic, butyric, and caproic acids
Acetic F.A. (2C ) CHAcetic F.A. (2C ) CH
33-COOH-COOH
Butyric F.A. (4C ) CHButyric F.A. (4C ) CH
33-(CH-(CH
22))
22-COOH-COOH
Caproic F.A. (6C ) CHCaproic F.A. (6C ) CH
33-(CH-(CH
22))
44-COOH-COOH
17

18. b-Non-volatile short-chain fatty acids:
They are solids at room temperature and contain They are solids at room temperature and contain 7-107-10
carbon atomscarbon atoms
 They are water-soluble and non-volatile at room They are water-soluble and non-volatile at room
temperature include caprylic and capric F.A.temperature include caprylic and capric F.A.
Caprylic (8 C ) CH
3
-(CH
2
)
6
-COOH
Capric (10 C ) CH
3
-(CH
2
)
8
-COOH
18

19. B. Long-chain saturated 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) CH
3
-(CH
2
)
14
-COOH
 Stearic (18 C ) CH
3-(CH
2)
16-COOH
 Lignoceric (24C ) CH
3-(CH
2)
22-COOH
19

20. B-Unsaturated Fatty Acids
They contain double bond
Monounsaturated
They contain one double bonds--(C
nH
2n-1 COOH)
Polyunsaturated

They contain more than one double bond
(C
nH
2n-more
than 1 COOH)
20

21. I. Mono-unsaturated fatty acids:
. 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
CH
3-( CH
2 )
5CH = CH-(CH
2)
7 –COOH
21

22. 2. Oleic acid
 Is the most common fatty acid in natural fatsIs the most common fatty acid in natural fats
 It is It is C18:1∆9, i.e., has 18 carbons and one double i.e., has 18 carbons and one double
bond located at carbon number 9 and involving bond located at carbon number 9 and involving
carbon 10carbon 10

CH
3-(CH
2)
7- CH=CH – (CH
2)
7-COOH
22

23. 3. Nervonic acid
(Unsaturated lignoceric acid)
It is C24:115, i.e., has 24 carbons and one double
bond located at carbon number 15 and involving
carbon 16
CH
3
– (CH
2
)
7
CH= CH – (CH
2
)
13
- COOH
23

24. II. Polyunsaturated fatty acids, PUFAs
 Are usually referred as essential FAs
 The essentiality of fatty acids has been known
since the late 1920s
 Since the 1970s, evidence has accumulated
illustrating the essentiality PUFAs
24

25. Not all PUFAs are essential FAs
 some can be derived from other PUFAs
Source of PUFAs include:
 Vegetable oils and many other plant oils, cod liver oil and
animal fats
25

26. The double bonds in natural PUFAs are separated
by at least one methylene group
The C=C double bonds in almost all naturally
occurring fatty acids have a cis configuration
There are cases where trans double bonds are
known, however, these are seldom found in
membranes
26

27. Trans Fatty Acids
Nomenclature differs from normal cis FAs
only in the configuration of the double bonds
The three main origins of trans FAs in our diet
are
 Bacteria,
 Deodorized oils, and
 Partially hydrogenated oils
27

28. Physico-chemical properties FA
Physical Properties
The physical properties of fatty acids are largely
determined by the length and degree of
unsaturation of the hydrocarbon chain
28

29. Physical Properties of FAs (Length)
The longer the fatty acid chain length,
The poorer the solubility in water
The higher the melting point
The polar nature of the carboxylic acid group
accounts for the moderate solubility of short-
chain (<10 Cs) fatty acids in water
29

30. The fewer the double bonds in a fatty acid
The lower the solubility in water
The higher the melting point
30

31. Chemical Properties- reactions of FAs
A.R
x
ns due to the carboxylic acid include:
1.Salt formation – produce soap
2.Ester formation – formations of fats and oils
3.Amide formation - in sphingolipids
31

32. 32

33. 33
Oils and Fats
Major Component (%95-99)
Triglycerides
Minor Components (%1-5)
Triglyceride Derivatives
Glycerol
Free Fatty Acids
Mono- and Diglycerides
Non-Triglyceride Derivatives
Phospholipids
Sterols
Pigments
Vitamins
Antioxidants
Oxidation Products
Trace Metals
Hydrocarbons

34. Saturated

Solids at room temperature

Found in meat and dairy products
Are bad for health

Increase cholesterol levels - can lead to heart
problems
34

35. Common
name
Chemical
structure
C:D
Caprylic acidCH
3
(CH
2
)
6
COOH 8:0
Capric acid CH
3(CH
2)
8COOH 10:0
Lauric acid CH
3(CH
2)
10COOH 12:0
Myristic acidCH
3(CH
2)
12COOH 14:0
Palmitic acidCH
3
(CH
2
)
14
COOH 16:0
Stearic acid CH
3
(CH
2
)
16
COOH 18:0
Arachidic acidCH
3
(CH
2
)
18
COOH 20:0
Behenic acid CH
3
(CH
2
)
20
COOH 22:0
Lignoceric acidCH
3(CH
2)
22COOH 24:0
Cerotic acid CH
3
(CH
2
)
24
COOH 26:0
35

36. Mono unsaturated
 Contain just one C=C
 Thet are important to our health(lower cholesterol
leve)
 Found in groundnut oil, avocados
 Both MUFAs and PUFAs are important to
our health, they lower cholesterol level
36

37. Poly unsaturated
Are considered to be ‘good fats’
Contain more than one C=C bond
Tend to be liquids at room temperature, eg
olive oil
Include two important types

Omega 3 - fatty acids

Omega 6 - fatty acids
37

38. Omega 3 - fatty acids
Lower the total amount of fat in the blood and can
lower blood pressure and decrease the risk of
cardiovascular disease
Example: Eicosapentaenoic acid-(EPA,20:5-
Δ5,8,11,14,17)
Docosahexaenoic acid-(DHA, 22:6-
Δ4,7,10,13,16,19
38

39. Omega 6 - fatty acids
 Reduce the risk of cardiovascular disease but
can contribute to allergies and inflammation
39

40. Decomposition products of fatty acids
1. Linoleic acid:
C18:29, 12.
 It is the most important since other essential fatty
acids can be synthesized from it in the body.
CH
3
-(CH
2
)
4
-CH = CH-CH
2
-CH=CH-(CH
2
)
7
-COOH
40

41. 2. Linolenic acid:
C18:39, 12, 15,
In corn, linseed, peanut, olive, cottonseed and soybean
oils
CH
3-CH
2-CH=CH-CH
2-CH=CH-CH
2-
CH=CH-(CH
2)
7-COOH
41

42. 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
CH
3-(CH
2)
4-CH=CH-CH
2-CH=CH-CH
2CH=CH-
CH
2
-CH=CH-(CH
2
)
3
-COOH
42

43. Function of Essential Fatty Acids:
1.Useful in the treatment of atherosclerosis
(transporting blood cholesterol and triglycerides)
2.Many important 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
43

44. Composed of fatty acids and alcohol
components
 Include
 Acylglycerols
 Ether acylglycerols
 Sterols and their esters and
 Wax esters
44

45. A. Acylglycerols
Are the predominant constituent in oils and fats
of commercial importance
Glycerol
 Can be esterified with one, two, or three fatty
acids, and
 The individual fatty acids can be located on
different carbons of glycerol
45

46. The terms:
 monoacylglycerol, diacylglycerol, and
triacylglycerol are preferred to the older names
mono-, di-, and triglycerides
46

47. Triglycerides (Neutral Fats and oils)
A large proportion of FAs in biological systems
exist as TGs

This is the primary storage form of body fat

TGs are the most common component of fats
and oils
47

48. Cont.…Cont.…
48
H
2
CO
CHO
H
2
C
C
C
OC
R
1
R
3
R
2
O
O
O
+
3 H
2O
CH
2
OH
CHHO
CH
2
OH
HOCR
1
O
HOCR
3
O
HOCR
2
O
Fatty acids
Glycerol
Triglycerides
(Triacylglycerol)

49. 1-Simple triglycerides1-Simple triglycerides: If the three fatty acids : If the three fatty acids
connected to glycerol are of the same type the connected to glycerol are of the same type the
triglyceride is called simple triglyceride, e.g., triglyceride is called simple triglyceride, e.g.,
tripalmitintripalmitin
2-Mixed triglycerides2-Mixed triglycerides: if they are of different types, : if they are of different types,
it is called mixed triglycerides, e.g., stearo-diolein it is called mixed triglycerides, e.g., stearo-diolein
and palmito-oleo-stearinand palmito-oleo-stearin
 Natural fats are mixtures of mixed triglycerides Natural fats are mixtures of mixed triglycerides
with a small amount of simple triglycerideswith a small amount of simple triglycerides
49

50. CH
2
O
CHO
CH
2
C
C
OC
(CH
2
)
14
O
O
O
Tripalmitin
(simple triacylglycerol)
CH
3
(CH
2
)
14
CH
3
(CH
2
)
14
CH
3
CH
2
O
CHO
CH
2
C
C
OC
(CH
2
)
16
O
O
O
1-Stearo-2,3-diolein
(mixed triacylglycerol)
CH
3
(CH
2
)
7
CHCH(CH
2
)
7
CH
3
(CH
2
)
7
CHCH(CH
2
)
7
CH
3
CH
2
O
CHO
CH
2
C
C
OC
(CH
2
)
14
O
O
O
1-palmito-2-oleo-3-stearin
(mixed triacylglycerol)
CH
3
(CH
2
)
16
CH
3
(CH
2
)
7
CHCH(CH
2
)
7
CH
3
50

51.  The commonest fatty acids in animal fats are The commonest fatty acids in animal fats are
palmitic, stearic and oleic acids
The main difference between fats and oils is The main difference between fats and oils is oils oils
are being liquidsare being liquids at room temperature, whereas, at room temperature, whereas,
fats are solidsfats are solids
 This is mainly due to presence of larger This is mainly due to presence of larger
percentage of percentage of unsaturated fatty acids in fatty acids in oilsoils than than
fatsfats that has mostly that has mostly saturated fatty acids fatty acids
51

52. Because of their high degree of order,
saturated FAs pack together well
As a result both saturated fatty acids and
triglycerides derived from them are solids at
room temperature
52

53. Unsaturated FAs not pack as well in a crystal
lattice as their saturated counterparts,
Butter fat, for example, has a high content of
saturated fatty acids and is a solid at room
temperature
Salad oils (from plant oils) have a high content of
polyunsaturated fatty acids and are liquid at room
temperature
53

54. Melting points of fats are usually low
Melting points and boiling points are not usually
sharp (most fats/oils are mixtures)
When shaken with water, oils tend to emulsify
54

55. Physical properties of fat and oils: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
55

56. Reactions of fats and oilsReactions of fats and oils:
1-Hydrolysis:1-Hydrolysis:
They are hydrolyzed into their constituents (They are hydrolyzed into their constituents (fatty acids and fatty acids and
glycerol)glycerol) by the action of super heated steam, acid, alkali or by the action of super heated steam, acid, alkali or
enzyme (e.g., lipase of pancreas)enzyme (e.g., lipase of pancreas)
- During their enzymatic and acid hydrolysis glycerol and - During their enzymatic and acid hydrolysis glycerol and
free fatty acids are producedfree fatty acids are produced
56
CH
2
O
CHO
CH
2
C
C
OC
R
1
R
3
R
2
O
O
O
3 H
2
O
H
2
COH
CHHO
H
2
COH
OHCR
1
O
OHCR
3
O
+
OHCR
2
OLipase or Acid
Triacylglycerol
Glycerol
Free fatty acids

57. 2. 2. SaponificationSaponification. .
Alkaline hydrolysis produces glycerol and salts of Alkaline hydrolysis produces glycerol and salts of
fatty acids (fatty acids (soaps)
Soaps cause emulsification of oily material this help Soaps cause emulsification of oily material this help
easy washing of the fatty materialseasy washing of the fatty materials
Saponification reactionSaponification reaction
57

58. 3. Addition
Neutral fats containing unsaturated FAs have the
ability of adding hydrogen or halogens at the
double bonds
e.g., hydrogen or hydrogenation and iodine or
iodination
58
HH
H
2

59. a. Hydrogenation
It is a type of addition reactions accepting
hydrogen at the double bonds of unsaturated
fatty acids.
It can take place
Artificially: food processing
Naturally: Rumen biohydrogenation (via microbial
metabolism)
59

60. b. Halogenation
Neutral fats containing unsaturated fatty acids have
the ability of adding halogens (e.g., 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
60
CH(CH
2
)
7
COOHCHCH
2
CH
Linoleic acid
CH(CH
2
)
4
CH
3
2 I
2
CH(CH
2
)
7
COOHCHCH
2
CH
Stearate-tetra-iodinate
CH(CH
2
)
4
CH
3
II I I

61. Advantages of hydrogenated oil or fat are as
follows:
1.1.It is more pleasant as cooking fatIt is more pleasant as cooking fat
2.2.It is digestible and utilizable as normal animal It is digestible and utilizable as normal animal
fats and oilsfats and oils
3.3.It is less liable to cause gastric or intestinal It is less liable to cause gastric or intestinal
irritationirritation
4.4.It is easily stored and transported and less liable It is easily stored and transported and less liable
to rancidityto rancidity
Disadvantages of hydrogenation
Inability to obtain fat-soluble vitamins (A, D, E Inability to obtain fat-soluble vitamins (A, D, E
and K) and essential fatty acidsand K) and essential fatty acids
61

62. 4. Oxidation
This toxic reaction of TGs leads to unpleasant
odour or taste of oils and fats developing after
oxidation by oxygen of air, bacteria, or moisture
62
Lipid peroxidation

63. Lipid peroxidation
A non-enzymatic reaction catalyzed by oxygen
May occur in tissues or in foods (spoilage)
The hydroperoxide formed is very reactive and leads
to the formation of free radicals which oxidize
protein and/or DNA (causes aging and cancer)
The principle is also used in drying oils to form hard
films
Example is linseed oil, which is used in paints and
varnishes manufacturing
63

64. WaxesWaxes
Waxes (commonly called wax esters) are esters of
fatty acids and long chain alcohols
Waxes are widely distributed in nature such as the
secretion of certain insects as bees-wax, protective
coatings of the skins of animals, leaves and fruits of
plants
64

65. Structure
Waxes are simple esters of fatty acids (usually
saturated with long chain monohydroxy alcohols)
65
H
3C (CH
2)
14 C O
H
2
C
O
(CH
2)
28 CH
3
Fatty acid Long chain alcohol

66. Simple waxes
Are solids containing a monohydric alcohol (with a
higher molecular weight than glycerol) esterified to
long-chain FAs
Are usually esters of medium chain FAs (16:0, 18:0,
18:1ω9) and long chain aliphatic alcohols
Examples of these alcohols are palmitoyl alcohol,
cholesterol, vitamin A or D
The alcohols range in size from C8 to C18
Are found on the surface of animals, plants, and insects and
play a role in prevention of water loss
66

67. Simple waxes can be named by removing the -ol
from the alcohol and replacing it with -yl, and
replacing the -ic from the acid with -oate
For example, the wax ester from hexadecanol and
oleic acid would be named hexadecyl oleate or
hexadecyl-cis-9-hexadecenoate

67

68. The C16 alcohol (1-hexadecanol) is commonly
called cetyl alcohol
Thus, cetyl oleate is another acceptable name for
this compound
Waxes of importance in foods as additives include
beeswax, carnauba wax
Complex waxes:
Are formed from diols or alcohol esters
68

69. 69
Bee’s wax
Carnauba wax source

70. Properties of waxes:
Waxes are

Insoluble in water, but soluble in fat solvents

Not easily hydrolysable as fats

Negative for acrolein testNegative for acrolein test

Indigestible by lipases

Very resistant to rancidity
Thus they are of no nutritional value
70

71.  Waxes typically have fairly high melting points,
especially when compared to TGs
 Certain skin glands of vertebrates secrete waxes to
protect hair, skin and keep it flexible, lubricated, and
waterproof
71

72. Definition:
They are lipids that contain additional
substances, e.g.,

Sulfur,

Phosphorus,

Amino group,

Carbohydrate, or

Proteins beside FA and alcohol
72

73. Compound or conjugated lipids are classified into
the following types according to the nature of the
additional group:
1.Phospholipids
2.Glycolipids
3.Lipoproteins
4.Sulfolipids and amino lipids
73

74. 74

75. Fat constants or numbers are tests used for:
1.Checking the purity of fat for detection of
adulteration (mixing of impurity)
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
75

76. 1-Iodine number (or value):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 (no. of I no.
of double bonds), detection of adulteration and determining
the biological value of fat
76

77. Example of iodine number of some oils
oCottonseed oil: 103 –111
oOlive oil: 79 – 88
oLinseed oil: 175 –202
77

78. 2-Saponification number (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 Since each carboxyl group of a fatty acid reacts
with one with one mole of KOH during saponification, the
amount of alkali needed to saponify certain weight
of fat depends upon the number of fatty acids
present per weight
78

79. 3. Acids Number (value):
Definition:
It is the number of It is the number of milligrams of KOH required required
to neutralize the free fatty acids present in to neutralize the free fatty acids present in one
gram of fatof fat
Uses:
It is used for detection of hydrolytic rancidity It is used for detection of hydrolytic rancidity
(bad odour due to FFAs)because it measures the (bad odour due to FFAs)because it measures the
amount of free fatty acids presentamount of free fatty acids present
79

80. 4-Acetyl Number (or value):
Definition:
It is number It is number of milligrams of KOH needed to needed to
neutralize the acetic acid liberated from hydrolysis of neutralize the acetic acid liberated from hydrolysis of
1 gram of acetylated fat ((hydroxy fat reacted with hydroxy fat reacted with
acetic anhydrideacetic anhydride)
80

81. Differences between neutral lipids and waxes :
Waxes Neutral lipids
1.Digestibility: Indigestible (not Indigestible (not
hydrolyzed by lipase).hydrolyzed by lipase).
Digestible (hydrolyzed by lipase).Digestible (hydrolyzed by lipase).
2-Type of
alcohol:
Long-chain monohydric Long-chain monohydric
alcohol + one fatty acid.alcohol + one fatty acid.
Glycerol (trihydric) + 3 fatty acidsGlycerol (trihydric) + 3 fatty acids
3-Type of fatty
acids:
Fatty acid mainly palmitic Fatty acid mainly palmitic
or stearic acid.or stearic acid.
Long and short chain fatty acids.Long and short chain fatty acids.
4-Acrolein test:Negative.Negative. Positive.Positive.
5-Rancidability:Never get rancid.Never get rancid. Rancidible.Rancidible.
6-Nature at
room
temperature.
Hard solid.Hard solid. Soft solid or liquid.Soft solid or liquid.
7-SaponificationNonsaponifiable.Nonsaponifiable. Saponifiable.Saponifiable.
8-Nutritive
value:
No nutritive value.No nutritive value. Nutritive.Nutritive.
9-Example: Bee & carnuba waxes.Bee & carnuba waxes. Butter and vegetable oils.Butter and vegetable oils.
81

82. T
h
e

e
n
d
!
!
!