Lipids are a diverse group of organic molecules that play essential roles in living organisms. They are characterized by their hydrophobic nature, meaning they are not soluble in water. The main classes of lipids include triglycerides (fats and oils), phospholipids, steroids, and waxes. 1. **Triglycerides:** These are the most common type of lipids and serve as a major energy storage form in cells. Triglycerides consist of glycerol and three fatty acid chains. Fatty acids can be saturated (no double bonds) or unsaturated (contain double bonds), influencing the physical properties of the lipid. 2. **Phospholipids:** These molecules are crucial components of cell membranes. Similar to triglycerides, they consist of glycerol and fatty acids, but one of the fatty acid chains is replaced by a phosphate group. The hydrophilic (water-attracting) phosphate head and hydrophobic (water-repelling) fatty acid tails contribute to the formation of the lipid bilayer in cell membranes. 3. **Steroids:** Steroids have a unique structure and play various roles in the body, including serving as structural components of cell membranes and acting as signaling molecules. Cholesterol is a common steroid and is a precursor to hormones like estrogen and testosterone. 4. **Waxes:** Waxes are esters of long-chain fatty acids and long-chain alcohols. They often function as protective coatings for plants and animals, helping to reduce water loss and prevent damage. Lipids serve several vital functions in living organisms: - **Energy Storage:** Triglycerides store energy in a concentrated form and can be broken down to release energy when needed. - **Structural Role:** Phospholipids form the basis of cell membranes, providing structure and regulating the passage of substances into and out of cells. - **Insulation and Protection:** Fats can act as insulators, helping organisms retain heat. Waxes form protective coatings on surfaces. - **Cell Signaling:** Some lipids, such as certain steroids, serve as signaling molecules that regulate various physiological processes. In summary, lipids are a diverse group of molecules with varied structures and functions, crucial for the structure, function, and energy balance of living organisms.

1. Lecture XI
Aqsa Akhtar
School of Food and Agricultural Sciences
University of Management andTechnology
FST-2101 3(3-0)
Food Chemistry
1

2. Lipids 1
LectureTitle

3. Session 11: Learning Outcomes
Learning Objective
▪ Differentiate between major and minor food components and their
functions and physiochemical properties
Learning Outcome
▪ Explain the properties and reactions of carbohydrates, lipids,
proteins, and enzymes during the storage and processing of food
Session Learning Outcomes
▪ SLO 11.1: Understand the structures, chemistry, and functions of
different fatty acids
▪ SLO 11.2: Explain the classification of different of fatty acids based on
carbon numbers and double bonds

4. Introduction
▪ Heterogeneous class of naturally occurring organic substances
▪ Have a distinguished functional group or structural features
▪ Insoluble in water and highly soluble in organic solvents; ether,
chloroform, benzene, and acetone
▪ This property sets them apart from proteins, carbohydrates,
nucleic acids and other biomolecules
▪ Widely distributed in the biological world
▪ Play a wide variety of roles in plant and animal tissues
Lipids (Greek: lipos, means fat or lard)

5. Functions of Lipids
Lipids are a concentrated source of energy
One gram of fat gives 9 Kcal
Lipids serve as a cushion for the vital organs and protects
them from external shocks or injuries
Lipids are the structural materials of cells and membranes
Lipids serve as insulator for our body
Lipids are the carrier/reservoir of fat soluble vitamins
In food preparations, lipids serve as a binding agent
Lipids also enhance the palatability of foods

6. Fatty Acids
▪ Building blocks for triglycerides and phospholipids
▪ A chain of carbon and hydrogen atoms with a carboxyl group
(COOH) at the alpha end and a methyl group (CH3) at the
omega end

7. Fatty Acids andTypes
▪ Fatty acids are structural components of all the lipids
▪ They are naturally occurring monocarboxylic acids that tend to have
even numbers of carbon atoms and may be classified as:
➢Long-chain (C12 to C26)
➢Medium-chain (C8 to C10)
➢Short-chain (C4 to C6)
Fatty acids are not like most lipids in that they may be recognized
distinctly by the presence of a COOH group on a carbon chain

8. Fatty Acids andTypes (Contd.)
▪ Fatty acids may also be categorized with regards to the presence
(and number) of unsaturated units (double bonds)
▪ Saturated fatty acids (SFAs) contain no double bonds – all C-
C single bonds in the carbon chain component.

9. Saturated Fatty Acids
▪ The packing of fatty
acids depends on
their degree of
saturation
▪ Stearic acid is shown
here in its usual
extended
conformation
▪ Saturated fatty acids
are tightly packed
and stabilized by
many hydrophobic
interactions
Fatty Acids andTypes (Cont.)

10. Unsaturated Fatty Acids ▪ The double bond (shaded)
introduces a rigid bend in the
hydrocarbon tails
▪ Fatty acids with one or
several such bends cannot
pack together as tightly as
saturated fatty acids
Fatty Acids andTypes (Cont.)

11. Fatty Acids andTypes (Cont)
▪ Monounsaturated fats (MUFAs) possess one C-C double bond in a
monocarboxylic acid structure, and nearly all naturally occurring MUFAs
have cis- cis-stereochemistry

12. Fatty Acids andTypes (Cont.)
▪ Polyunsaturated fatty acids (PUFAs) possess more than one
double bond in the carbon chain component of the fatty acid
▪ Up to six double bonds may be found in biochemically important PUFAs
Fatty acids typically have the following characteristics:
✓ An unbranched carbon chain
✓ An even number of carbon atoms in the chain
✓ When double bonds are present, they have cis-stereochemistry

13. Fatty Acids andTypes (Cont.)
▪ A system exists for describing unsaturated fatty acids in terms of the
number of carbon atoms in the acid and in terms of double bond
position(s)
16:0
Fatty acid with 16 C-atoms
and no double bonds
18:1 D9
Fatty acid with 18 C-atoms
and one double bond at C-9
18:3 D9,12,15
Fatty acid with 18 C-atoms
and three double bonds at
C-9, C-12, and C-15

14. Fatty Acids andTypes (Contd.)
• Several families of unsaturated fats may be recognized by the number
of saturated carbon atoms that follow the last double bond (the
placement of the methyl end of the chain concerning the double bond),
Omega fatty acids
1
2
3
1
2
3
4
5
6
ω-3 (omega-3 fatty acid)
ω-6 (omega-6 fatty acid)

15. ▪ The location of the first double bond in unsaturated fatty acids
affects the naming and characteristics of the unsaturated fatty acids
▪ Omega-3 fatty acid
▪ The first double bond is between the third and fourth carbon from the
omega end
▪ Example:Alpha-linolenic acid (ALA) (One of the two essential fatty acids)
▪ Omega-6 fatty acid
▪ The first double bond is between the sixth and seventh carbon from the
omega end
▪ Example: Linoleic acid (One of the two essential fatty acids)

16. Saturated Fatty Acids Examples
Unsaturated Fatty Acids Examples

17. Cis and Trans Fatty Acids
The natural configuration of double bonds in unsaturated fatty acids is the cis
configuration
In the cis configuration, the carbons of the aliphatic chain are on the same side of
the double bond, while trans double bonds have the carbons on opposite sides
PUFAs with over two double bonds usually have a pentadiene configuration
In a pentadiene system, the two double bonds are separated by a methylene-
interrupted carbon and are not conjugated
This means that the double bonds of most unsaturated fatty acids are three
carbons apart (e.g., 9, 12, 15 octadecatrienoic)

18. Cis and Trans Fatty Acids (Cont)

19. Cis and Trans Fatty Acids (Cont)

20. Saturated and Unsaturated Fatty Acids Help
Shape Food

21. Questions/Discussion 21