1. Lipid

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

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

5. Biological Importance of Lipids
They are more palatable and storable to unlimited amount compared to carbohydrates.
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.
Supply the essential fatty acids that cannot be synthesized by the body.
Supply the body with fat-soluble vitamins (A, D, E and K).
They are important constituents of the nervous system.
Tissue fat is an essential constituent of cell membrane and nervous system. It is mainly phospholipids in nature that are not affected by starvation.

6. Fatty Acid Structure - H - H = O H - C - ( C )n - C - OH - H - H
Carboxyl group
- H
- H
Carbon group(s)
Methyl group

7. Fatty Acid and Lipids Key building blocks for lipids
Chains of carbon atoms with a carboxyl group at one end, and a methyl group at the other
May be “free” or attached to another compound
Determine the characteristics of the fat

8. Fatty Acid Chain Length
Short chain: 2 to 6 C (volatile fatty acids)
Medium chain: 8 – 12 C
Long chain: 14 – 24 C
As chain length increases, melting point increases
Fatty acids synthesized by plants and animals have an even number of carbons
Mostly long chain
16C to 18C fatty acids are most prevalent

9. Fatty Acid Saturation Saturated - no double bonds
Unsaturated – contain double bonds
Monounsaturated – one double bond
Polyunsaturated - >1 double bond
The double bond is a point of unsaturation
As number of double bonds increases, melting point decreases

10. Saturated Fats
All the chemical bonds between the carbon are single bonds C-C-C-
No double bonds
No space for more H atoms; fully “saturated”
Solid at room temperature
Butter, shortening, lard, coconut oil, palm oil, and fully hydrogenated vegetable oils
Poultry skin, whole milk

11. Mono-Unsaturated Fatty Acids
Only one double bond
Therefore, two H atoms can be added
Liquid at room temperature
Olive oil, canola oil, peanut oil
Other sources: avocado, almonds, cashews, pecans and sesame seeds (tahini paste)

12. Poly-Unsaturated Fatty Acids
Two or more double bonds
Include omega-3 and omega-6 fatty acids (essential fatty acids)
Linolenic acid: omega 3 fatty acid
Linoleic acid: omega 6 fatty acid
Richest sources of poly-unsaturated fatty acids include:
Vegetable oils
Corn, sunflower, safflower, cotton seed oils

13. Fatty Acid Synthesis Issues
Ω-3
Ω-6
Ω-9
C-C-C=C-C-C=C-C-C=C-C-C-C-C-C-C-C-COOH
Animals can synthesize a fatty acid with a double bond in the omega 9 position but not at either 3 or 6 positions
Omega-3 and omega-6 fatty acids must be derived from diet
Cold water fish accumulate high levels of omega 3 fatty acids from their diet

14. Omega System and Essential Fatty Acids
Linoleic acid is an omega-6 fatty acid
Linolenic and arachidonic acids are omega-3 fatty acids
Linoleic and linolenic acids are essential fatty acids
Arachidonic acid can be synthesized from linoleic acid, so not essential

15. Arachedonic Acid
Linoleic Acid

16. Acids
Carbons
Double bonds
Abbreviation
Source
Acetic 2
2:0
bacterial metabolism
Propionic 3
3:0
Butyric 4
4:0
butterfat
Caproic 6
6:0
Caprylic 8
8:0
coconut oil
Capric 10
10:0
Lauric 12
12:0
Myristic 14
14:0
palm kernel oil
Palmitic 16
16:0
palm oil
Palmitoleic 1
16:1
animal fats
Stearic 18
18:0
Oleic
18:1
olive oil
Linoleic
18:2
grape seed oil
Linolenic
18:3
flaxseed (linseed) oil
Arachidonic 20
20:4
peanut oil, fish oil

17. Types of Fatty Acid
Fatty Acids are two types according to the function
Essential Fatty Acids
Non-essential fatty acids

18. 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

19. 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.
symptoms :
poor growth and health with susceptibility to infections, dermatitis, decreased capacity to reproduce, impaired transport of lipids, fatty liver, and lowered resistance to stress.

20. Function of Essential Fatty Acids
They are useful in the treatment of atherosclerosis by help transporting blood cholesterol and lowering it and transporting triglycerides.
The hormones are synthesized from them.
They enter in structure of all cellular and subcellular membranes and the transporting plasma phospholipids.
They are essential for skin integrity, normal growth and reproduction.
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.

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

22. CH3-(CH2)4-CH=CH-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)3-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-CH2-CH=CH-CH2-CH=CH-(CH2)3-COOH

23. 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.

24. Properties of Glycerol
Colorless viscous oily liquid with sweet taste.
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.

25. 3- It combines with three molecules of nitric acid to form trinitroglycerin (TNG) that is used as 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.

26. Uses of Glycerol
Glycerol enters in pharmaceutical and cosmetic preparations.
Reduces brain edema in cerebrovascular disease.
Nitroglycerin is used as vasodilator especially for the coronary arteries, thus it is used in treatment of angina pectoris. Also, enters in explosives manufacturing.
Glycerol is used in treatment of glaucoma (increased intraocular pressure)due to its ability to dehydrate the tissue from its water content.

27. 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.

28. Classification of Lipids
Simple lipids (Fats & Waxes)
Compound or conjugated lipids
Derived Lipids

29. Simple Lipids Neutral fats and oils Triacyl glycerols (triglycerides)
Monoacyl glycerols (monoglycerides)
Diacyl glycerols (diglycerides)
Diglycerides found in plant leaves
One fatty acid is replaced by a sugar (galactose)
Triacyl glycerols (triglycerides)
Lipid storage form
Most lipids consumed are triglycerides
Triglycerides found in seeds and
animal adipose tissue

30. Triglycerides Most common structure in dietary lipids
Composed of one glycerol molecule and three fatty acids connected by an ester bond (bond between an alcohol and and organic acid)
Fatty acids may be same or mixed
Fatty Acid
Fatty Acid
Glycerol
Fatty Acid

31. Triglyceride Structure
Fatty acid composition of triglyceride varies according to function
Membrane lipids must be fluid at all temperatures
Contain more unsaturated fatty acids
Lipids in tissues subjected to cooling (e.g., hibernators or tissues in extremities)
Contain more unsaturated FAs

32. Most Common Fatty Acids in Di- and Triglycerides
Carbon:Double bonds
Double bonds
Myristic
14:0
Palmitic
16:0
Palmitoleic
16:1
Cis-9
Stearic
18:0
Oleic
18:1
Linoleic
18:2
Cis-9,12
Linolenic
18:3
Cis-9,12,15
Arachidonic
20:4
Cis-5,8,11,14
Eicosapentaenoic
20:5
Cis-5,8,11,14,17
Docosahexaenoic
22:6
Cis-4,7,10,13,16,19
CH3(CH2)nCOOH

33. Compound Lipids
They are lipids that contain additional substances, e.g., sulfur, phosphorus, amino group, carbohydrate, or proteins beside fatty acid and alcohol.
Compound or conjugated lipids are classified into the following types according to the nature of the additional group:
Phospholipids
Glycolipids.
Lipoproteins
Sulfolipids and amino lipids.

34. Phospholipids Definition:
Phospholipids or phosphatides are compound lipids, which contain phosphoric acid group in their structure.
Importance:
They are present in large amounts in the liver and brain as well as blood. Every animal and plant cell contains phospholipids.
The membranes bounding cells and subcellular organelles are composed mainly of phospholipids. Thus, the transfer of substances through these membranes is controlled by properties of phospholipids.
They are important components of the lipoprotein coat essential for secretion and transport of plasma lipoprotein complexes. Thus, they are lipotropic agents that prevent fatty liver.
Myelin sheath of nerves is rich with phospholipids.

35. Phospholipids Two primary types: Glycerophosphatides
Core structure is glycerol
Part of cell membranes, chylomicrons, lipoproteins
Sphingophosphatides
Core structure is sphingosine
Part of sphingomyelin

37. Phospholipids lecithin
Glycerophosphatides resemble triglyceride in structure except one of the fatty acids is replaced by a compound containing a phosphate group, or occasionally, nitrogen
Most prevalent is lecithin
lecithin

38. Phospholipid Significant use in food industry as emulsifiers
Lipids form emulsion in water
Phospholipid sources:
Liver, egg yolk,
Soybeans, wheat germ
Peanuts

39. Lipoproteins
Definition: Lipoproteins are lipids combined with proteins in the tissues. The lipid component is phospholipid, cholesterol or triglycerides. The holding bonds are secondary bonds.
They include:
Structural lipoproteins:
These are widely distributed in tissues being present in cellular and subcellular membranes. In lung tissues acting as a surfactant in a complex of a protein and lecithin. In the eye, rhodopsin of rods is a lipoprotein complex.
Transport lipoproteins:
These are the forms present in blood plasma. They are composed of a protein called apolipoprotein and different types of lipids. (Cholesterol, cholesterol esters, phospholipids and triglycerides). As the lipid content increases, the density of plasma lipoproteins decreases

40. b) Very low-density lipoproteins (VLDL) or pre--lipoproteins:
Chylomicrons:
They have the largest diameter and the least density. They contain 1-2% protein only and 98-99% fat. The main lipid fraction is triglycerides absorbed from the intestine and they contain small amounts of the absorbed cholesterol and phospholipids.
b) Very low-density lipoproteins (VLDL) or pre--lipoproteins:
Their diameter is smaller than chylomicrons. They contain about 7-10% protein and 90-93% lipid. The lipid content is mainly triglycerides formed in the liver. They contain phospholipid and cholesterol more than chylomicrons.
c) Low-density lipoproteins (LDL) or -lipoproteins:
They contain 10-20% proteins in the form of apolipoprotein B. Their lipid content varies from 80-90%. They contain about 60% of total blood cholesterol and 40% of total blood phospholipids. As their percentage increases, the liability to atherosclerosis increases.

41. d) High-density lipoproteins (HDL) or -Lipoproteins:
They contain 35-55% proteins in the form of apolipoprotein A. They contain 45-65% lipids formed of cholesterol (40% of total blood content) and phospholipids (60% of total blood content). They act as cholesterol scavengers, as their percentage increases, the liability to atherosclerosis decreases. They are higher in females than in males. Due to their high protein content they possess the highest density.
e) Albumin-free fatty acids complex:
It is a proteolipid complex with 99% protein content associated with long-chain free fatty acids for transporting them.

42. Derived Lipids Prostaglandins Steroids Terpenes
Synthesized from arachidonic acid
Several metabolic functions
Steroids
Cholesterol, ergosterol, bile acids
Terpenes
Made by plants
Carotenoids, xanthophylls

43. Sterols Compounds with multi-ring structure Insoluble in water
Present both in plant and animal foods
Major sterol is cholesterol
However, cholesterol is found only in animal products (manufactured in liver)
High content in organ meats and egg yolk

44. Common Sterol Compounds
Vitamin D3 (cholecalciferol)
Cholesterol (a sterol)
                                                                                                      
Stigmasterol (a phytosterol)
Testosterone (a steroid hormone)

45. Cholesterol
Source: -
It is synthesized in the body from acetyl-CoA (1gm/day, cholesterol does not exist in plants) and is also taken in the diet (0.3 gm/day as in, butter, milk, egg yolk, brain, meat and animal fat).
Importance: -
It is the most important sterol in animal tissues as free alcohol or in an esterified form (with linoleic, oleic, palmitic acids or other fatty acids).
Steroid hormones, bile salts and vitamin D are derivatives from it.
Tissues contain different amounts of it that serve a structural and metabolic role, e.g., adrenal cortex content is 10%, whereas, brain is 2%, others %.