Chemistry of Fats & Oils

CHEMISTRY OF OILS AND FATS

Definition A group of substances that in general are soluble in organic solvents, but are not soluble in water are called lipids. Oils & Fats are one class of lipid. They can be used for edible as well as non-edible purposes.

Roles of Food Lipids Energy Source  Source of essential fatty acids  Carrier of Fat Soluble Vitamins  Main Flavor Source of Foods  Regulates Hormone and Cell Structure  Help to Develop Nervous System  Build adipose tissues which cause Thermal Insulation of Body  Mouth Feeling  Texture of Foods  Emulsifying Agents  Mold Releasing and Anti-spattering Agent 

Source of Food Lipids



Plant source – seeds, grains, fruits, brans etc.



Animal source – milk, egg, tallow, lard, microbial etc.

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Marine source – fish and other animals.

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World Supply  –  Vegetable oil

68%

 –  Animal fat

28%

 –  Marine oil -

4%

Types of Lipids 1. Fatty acids 2. Neutral fats and oils or triglycerides 3. Monoglycerides and diglycerides 4. Waxes 5. Phospholipids 6. Sterols

Composition of fats and oils Fatty acid esters of glycerol i.e. triglycerides



Triglycerides which is liquid at room temperature are termed as oils and those solids are termed as fats



Triglycerides

O

O H2C

OH

HC

OH

H2C

OH

Glycerol

+

HO

C O

R 

HO

C O

R 

HO

C

R 

3 Fatty Acids

H2C

O

C O

R 

HC

O

C R  O

H2C

O

C

R 

+ 3 H2O

Saturated and Unsaturated Fatty Acids

Cis And Trans Fatty Acids

CH3 (CH2 )7

H

H

C

C

10

O (CH2 )7

9

C

OH

Cis 9 - Octadecenoic Acid (oleic)

H CH3 (CH2 )7

C

O C

(CH2 )7

C

H Trans 9 - Octadecenoic Acid (elaidic acid)

OH

Polyunsaturated Fatty Acids Linoleic acid:

Cis, cis, 9, 12 - Octadecadienoic acid

Linolenic acid: acid

Cis, cis, cis 9, 12, 15 - Octadecatrienoic

Arachidonic acid: Cis, cis, cis, cis 5, 8, 11, 14 Eicosatetraenoic acid Linoleic Acid Linolenic Acid Arachidonic Acid

 Naturally-occurring Fatty Acids

1.

Cis form

2.

Not conjugated (isolated) and conjugated (not very

common) double bonds. 3.

Even numbered fatty acids.

Fatty Acids Melting Points and Solubility in Water 

x t

Melting Point

ni o P g ni

x

M

x

x x

tl

x

e

x x z

Solubility in H O2

Fatty Acid Chain Length

Effects of Double Bonds on the Melting Points

M.P.

x x

x

# Double bonds

x

DIFFERENT TYPES OF GLYCERIDES H2 C HC H2 C

O

OH H2 C

OH O O

C

HC

(CH2 )16 CH3

H2 C

Monoglyceride (α - monostearin)

O

C

(CH2 )16 CH3

OH O O

C

(CH2 )16 CH3

Diglyceride (α, α' - distearin)

O H2 C

O

C O

(CH2 )16 CH3

( C18 )

HC

O

C O

(CH2 )14 CH3

(C16 )

H2 C

O

C

(CH2 )16 CH3

(C18 )

Triglyceride (β - palmityl distearin)

Fatty Acids (%) of Fats and Oils Fatty Acids

Butter

Coconut Cottonseed

Soybean

C 4 6

3

-

-

3

-

-

8

2

6

-

10

3

6

-

12

3

44

-

14

10

18

1

-

16

26

4

12

16:1

7

11 -

1

-

18:0

15

6

3

2

18:1

29

7

18

24

18:2

2

2

53

54

18 3

2

-

8

Phospholipid Lecithin (phosphatidyl choline) O O R

C

H2 C O

O

C

R 

CH CH3

O H2 C

O

P

O

O_  Phosphatidic Acid

CH 2

CH 2

N

+

CH3

CH3 Choline

Other phospholipids are : 

Phophatidyl ethanol amine

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Phosphatidyl serine

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Phosphatidyl inositol

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Cardiolipin

WAXES Esters of Fatty acid and Long chain alcohol

O C30 H61

O

C

O

C15 H 31

C16 H 33

O

C

C15 H 31

Sterols Plant sterols or PHYTOSTEROLS

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Animal Sterols or CHOLESTEROLS

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Phytosterol

Cholesterol 21

22

H3C

18 20

H3C 19

H 3C 2 3

HO

1 4

10

5

12 11 13 9

8

6 7

CH 3

17 14

16 15

CH 3

Characteristic Components Present on Some Special Oil 

Lignans in sesame oil;

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Oryzanol in rice bran oil;

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Gossypol in cottonseed oil;

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Cholesterol in butter as well as in animal fat;

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Hydroxy fatty acid in Castor oil;

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Cyclic acid in Sal fat;

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Trans fatty acid in Vanaspati

Non-lipid component present in Oils & Fats 

Fat soluble vitamins

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Pigments

Some important parameters to Characterize Fats and Oils

Analytical Methods 1. Acid Value 2. Saponification Value 3. Iodine Value 4. Peroxide Value 5. Gas Chromatographic Analysis for Fatty Acid composition 6. Liquid Chromatography for triglyceride composition

Acid Value  Number of mgs of KOH required to neutralize the Free Fatty Acid present in 1 g of oil/fat. Fatty acid generate due to hydrolytic rancidity Triglyceride

Moisture/

Fatty acids

Lipase

RCOOH + KOH

ROO K  + H2O -

+

AV = (56.1 x N x V)/ wt. of sample

Saponification Value Definition : mgs of KOH required to saponify 1 g of fat

Saponification - Hydrolysis of ester (triglyceride) under  alkaline condition. It gives the idea about the average molecular weight of fatty acid present in particular oil/fat. O H2 C HC H2 C

O O O

C O

R 

C O

R 

C

R 

H2 C

+

SP#=

3 KOH

Heat

56.1(B-S) x Nof HCl Gramof Sample

OH O

HC

OH

H2 C

OH

+

3R

C

-

+

O K 

Iodine Value gms of iodine absorbed by 100 g of oil. Iodine number indicates the amount of  unsaturation in fats and oils.

Iodine Value = (ml of Na2S2O3 volume for blank ml of Na2S2O3 volume for sample) Na2S2O3

0.127g/meq

100

Weight of Sample (g)

N of 

Peroxide Value It indicates about the amount of primary oxidation  products present in Oil/Fat.

Peroxide Value

=

ml of Na2S2O3 × Normality × 1000 Grams of Oil

Unit :

(mill equivalent /kg)

GC Analysis for Fatty Acids 1.

Extract fat.

2.

Saponify (hydrolysis under basic condition).

3.

Prepare methyl ester (by BF3-methanol/CH3ONa).

4.

Inject methyl ester in GC

5.

Determine peak areas of fatty acids. (Fatty acids are identified by relative retention time)

6.

Compare with response curve of standard.

Chromatogram of Fatty Acids Methyl Esters 18:1      e      s      n      o      p      s      e       R

14

16

18

18:2

18:3 20

21:1 22

 Time

GC condition: 10% DEGS Column (from supelco)

24

TAG Composition 

Triglyceride composition (e.g. S3, S2U, SU2 or  U3) of oil/fat can be determined by High Performance Liquid Chromatography (HPLC)

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In this chromatography, oil samples can be injected directly.

LIPID CONTENT ANALYSES

(1) Wet extraction For liquid samples (Milk, curd etc.)

(2) Dry extraction (Soxhlet Method) for  solid samples (seed, grain, bran etc.)

Soxhlet Method

Fat Soluble Vitamins

Vitamin A

H3 C

CH3

CH3

5

8 9

CH3

CH3

7

6

4

3

CH2OH 2

1

CH

3

H 3C

CH

H 3C

CH

3

3

Vitamin D2 H

H CH

2

HO

Vitamin E R 1 R 2 HO R 3

CH3 CH 3 O (CH2 CH2 CH2 CH2 )2 CH2 CH2CH2 CH(CH3 )2

Pigments β-Carotene and Chlorophyll (green)