1. Chapter IV (III part) Atmospheric oxidation Randicity
Reactions of the alkyl (SFA) and alkenyl (UFA) chain
Biological function of triglycerides

2. Atmospheric oxidation
Oxidation (Rancidty)
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

4. Lipid Oxidation
The important lipids involved in oxidation are the unsaturated fatty acid moieties, oleic, linoleic, and linolenic.
The rate of oxidation of these fatty acids increases with the degree of unsaturation.
Oleic – 1 times rate
Linoleic – 10 times
Linolenic – 100 times

5. Lipid Oxidation Initiation: RH + O2 -->R· + ·OH
R· + O2 --> · + ROO·
Propagation:
  ROO· + RH --> R· + ROOH
ROOH--> RO· + HO·
   
Termination:
R· + R· --> RR
R· + ROO·--> ROOR
ROO· + ROO· --> ROOR + O2

6. Lipid Oxidation of a Oleic Acid
oleic acid as an example, a hydrogen could be removed from either C-8 or C-10, as these positions are located alpha to the double bond.

7. The subsequent addition of abstracted hydrogen molecules results in the hydroperoxides shown

8. Lipid Oxidation of dienoic acid
The situation with a dienoic acid is a little different. While there are more positions a to a double bond, there is one position that is at two double bonds. This position is very reactive. For linoleic acid, carbon 11 is at two double bonds and will be removed to yield the free radical

9. Lipid Oxidation
Once formed, hydroperoxides may break down through a number of mechanisms. A common breakdown scheme is called dismutation. In this reaction a hydroperoxide reacts with another molecule or radical to form two new compounds.

10. Lipid Oxidation
This reaction scheme is capable of generating aldehydes, ketones, alcohols and hydrocarbons. Many of the volatile compounds formed during lipid oxidation originate through similar dismutations.

11. Lipid Oxidation
Both of these new radicals can initiate further oxidation. Some metals can speed up this reaction.

12. Lipid Oxidation

13. Measurement of lipid oxidation
Active Oxygen Method (AOM)
Iodine value or Peroxide Value is measured over time as Oxygen is bubbled through an oil sample
This method is also used to evaluate antioxidants

14. Antioxidants
Antioxidants function by interfering with the chain reaction. If the number of free radicals can be kept low enough, oxidation will not occur. The following is a model for the type of compound that can function effectively as an antioxidant:

15. Natural Antioxidants
Rosmariquinone

16. Natural Antioxidants Sesame Contains sesamol.
Oats Oats have been recognized to have antioxidant properties. Over 25 phenolic compounds have been identified in oats. Many derived from caffeic and ferulic acid.

17. Antioxidants Natural Antioxidants
Should not cause off flavors or colors
Must be lipid soluble
Must be non toxic
Should have carry through properties
Must be cost-effective

18. Rancidity
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.

19. Types and causes of Rancidity:
Hydrolytic rancidity
Oxidative rancidity
Ketonic rancidity
1-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.

21. 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.

23. 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.

24. Prevention of rancidity is achieved by:
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).
Removal of catalysts such as lead and copper that catalyze rancidity.
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.

25. Hazards of Rancid Fats:
The products of rancidity are toxic, i.e., causes food poisoning and cancer.
Rancidity destroys the fat-soluble vitamins (vitamins A, D, K and E).
Rancidity destroys the polyunsaturated essential fatty acids.
Rancidity causes economical loss because rancid fat is inedible.

26. Reactions of the alkyl (SFA) and alkenyl (UFA) chain

27. alkenyl (UFA) chain

28. Esterification
Saponification
Hydrolysis
(De)Hydrogenation
Alkoxylation
Pyrolysis
Halogenation
Addition

29. Functions of Triglycerides
contribute to the structure of membranes by the formation of a lipid bilayer.
phospholipid

30. aqueous interior of cell
aqueous exterior

32. Other Functions
There are several other useful functions of fats in the body.
They provide some protection against shock.
They also provide thermal insulation.
In foods they provide flavor and palatability.
Also, of course, they are used as a source of
energy.