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Rancidity &
Lipid
Peroxidation
Preshantha Govender
Roll #25
Biochemistry
Seminar
Shelf life
 The shelf life of a product refers to the
length of time a product may be stored
without becoming unsuitable ...
Examples of
products and their
shelf life stamps
What is Rancidity?
 Rancidity, is the natural process of
decomposition of fats or oils by either
hydrolysis or oxidation,...
Examples of rancid
food
Factors Causing Rancidity
 Catalysts: trace metal ions & inorganic
salts
 Temperature
 Amount of PUFA
 Time
 Light
 ...
Types of Rancidity
There are 3 types/pathways of rancidity:
1. Oxidative Rancidity
 Known as autoxidation
 It is due to ...
Example of oxidative rancidity
2. Hydrolytic Rancidity
 Known as hydrolysis/enzymatic oxidation.
 It is due to the contamination of fat by
lipase leadi...
Structures of TAG, DAG &
lipase enzyme
End products
aldehyde epoxide &
peroxide
3. Microbial Rancidity
 In which micro-organisms such as
bacteria, moulds and yeast use their
enzymes to break down chemi...
Structures of yeast,
mould spores &
bacteria
Lipid Peroxidation
 The main cause of rancidity of lipids is the
oxidative deterioration of lipids via a free-
radical ch...
Stage 1: Initiation
Molecular oxygen combines with
unsaturated fatty acids, producing
hydroperoxides and peroxyl free radi...
Stage 2: Propagation
This is when these unstable by-products of
the first stage react with other lipids, starting
a contin...
Stage 3: Termination
Is marked by the slowing or stopping of
reactions, completion of making unreactive
compounds or when ...
Diagram representing lipid peroxidation
Measuring Rancidity
Rancidity is most commonly detected by
taste or smell, but it is also accompanied by
a marked increase...
Harmful Effects of Rancid Food
 Leads to deficiencies such as anaemia,
hair loss & dermatitis.
 Kidney & heart disease
...
Examples of
anaemia, cancer
cells & dermatitis
Harmful Effects of Lipid
Peroxidation
 Damage to the cell membrane
 Cardiovascular diseases
 Joint diseases
 Ageing
 ...
Prevention of Rancidity
Prevention of Lipid
Peroxidation
Adding antioxidants (A, C & E) to one’s diet
retards lipid peroxidation.
References
Websites
 www.wikipedia.org
 www.cyberlipid.org
 www.slideshare.net
 www.naturalproductsinsider.com
Textboo...
Thank You 
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Rancidity & Lipid Peroxidation

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Seminar on rancidity and lipid peroxidation in biochemistry class, year 1 of medical school.

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Rancidity & Lipid Peroxidation

  1. 1. Rancidity & Lipid Peroxidation Preshantha Govender Roll #25 Biochemistry Seminar
  2. 2. Shelf life  The shelf life of a product refers to the length of time a product may be stored without becoming unsuitable for use or consumption.  After the shelf life of a product has reached, the food undergoes processes which results in rancidity.
  3. 3. Examples of products and their shelf life stamps
  4. 4. What is Rancidity?  Rancidity, is the natural process of decomposition of fats or oils by either hydrolysis or oxidation, or both.  The process of degradation converts fatty acid esters of oils into free fatty acids.  This gives rise to an unpleasant odour and taste in food.  These lipids degrade to the point of becoming either unpalatable or unhealthy to ingest.
  5. 5. Examples of rancid food
  6. 6. Factors Causing Rancidity  Catalysts: trace metal ions & inorganic salts  Temperature  Amount of PUFA  Time  Light  Water
  7. 7. Types of Rancidity There are 3 types/pathways of rancidity: 1. Oxidative Rancidity  Known as autoxidation  It is due to the auto-oxidation of PUFA present in triacylglycerols by the atmospheric O2 on free radicals.  The end product is the formation of aldehyde epoxide and peroxide.
  8. 8. Example of oxidative rancidity
  9. 9. 2. Hydrolytic Rancidity  Known as hydrolysis/enzymatic oxidation.  It is due to the contamination of fat by lipase leading to the formation of diacyl & triacylglycerols with free fatty acids.  The end product is the formation of aldehyde epoxide and peroxide.
  10. 10. Structures of TAG, DAG & lipase enzyme
  11. 11. End products aldehyde epoxide & peroxide
  12. 12. 3. Microbial Rancidity  In which micro-organisms such as bacteria, moulds and yeast use their enzymes to break down chemical structures in the oil, producing unwanted odours and flavours.  Water needs to be present for microbial growth to occur.  Can be prevented by sterilization
  13. 13. Structures of yeast, mould spores & bacteria
  14. 14. Lipid Peroxidation  The main cause of rancidity of lipids is the oxidative deterioration of lipids via a free- radical chain mechanism, which is also called lipid peroxidation.  This process occurs only within our bodies.  It occurs in three stages or phases: >Initiation >Propagation >Termination
  15. 15. Stage 1: Initiation Molecular oxygen combines with unsaturated fatty acids, producing hydroperoxides and peroxyl free radicals, both of which are highly reactive and unstable.
  16. 16. Stage 2: Propagation This is when these unstable by-products of the first stage react with other lipids, starting a continuing free radical lipid peroxidation chain reaction called autoxidation. This results in a continuing and cyclical oxidative degradation process, breaking down the lipid.
  17. 17. Stage 3: Termination Is marked by the slowing or stopping of reactions, completion of making unreactive compounds or when an antioxidant is added or encountered. There are two basic types of oxidative by-products, primary and secondary.
  18. 18. Diagram representing lipid peroxidation
  19. 19. Measuring Rancidity Rancidity is most commonly detected by taste or smell, but it is also accompanied by a marked increase in the acid value of the fat, which is tested by using two basic laboratory tests:  Peroxide Value (PV) for primary oxidation products  Anisidine Value (AnV) for secondary oxidation products.
  20. 20. Harmful Effects of Rancid Food  Leads to deficiencies such as anaemia, hair loss & dermatitis.  Kidney & heart disease  Neurodegeneration  Cancer
  21. 21. Examples of anaemia, cancer cells & dermatitis
  22. 22. Harmful Effects of Lipid Peroxidation  Damage to the cell membrane  Cardiovascular diseases  Joint diseases  Ageing  Cancer
  23. 23. Prevention of Rancidity
  24. 24. Prevention of Lipid Peroxidation Adding antioxidants (A, C & E) to one’s diet retards lipid peroxidation.
  25. 25. References Websites  www.wikipedia.org  www.cyberlipid.org  www.slideshare.net  www.naturalproductsinsider.com Textbooks  Textbook of medical biochemistry (8th Edition)  Principles of biochemistry (4th Edition)
  26. 26. Thank You 

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