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

1. Rancidity &
Lipid
Peroxidation
Preshantha Govender
Roll #25
Biochemistry
Seminar

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. Examples of
products and their
shelf life stamps

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. Examples of rancid
food

6. Factors Causing Rancidity
 Catalysts: trace metal ions & inorganic
salts
 Temperature
 Amount of PUFA
 Time
 Light
 Water

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. Example of oxidative rancidity

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. Structures of TAG, DAG &
lipase enzyme

11. End products
aldehyde epoxide &
peroxide

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. Structures of yeast,
mould spores &
bacteria

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. 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. 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. 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. Diagram representing lipid peroxidation

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. Harmful Effects of Rancid Food
 Leads to deficiencies such as anaemia,
hair loss & dermatitis.
 Kidney & heart disease
 Neurodegeneration
 Cancer

21. Examples of
anaemia, cancer
cells & dermatitis

22. Harmful Effects of Lipid
Peroxidation
 Damage to the cell membrane
 Cardiovascular diseases
 Joint diseases
 Ageing
 Cancer

23. Prevention of Rancidity

24. Prevention of Lipid
Peroxidation
Adding antioxidants (A, C & E) to one’s diet
retards lipid peroxidation.

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. Thank You 