Rancidity & Lipid Peroxidation

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 reach ed , 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: Oxidative Rancidity Known as autoxidation It is due to the auto-oxidation of PUFA present in triacylglycerols by the atmospheric O 2 on free radicals . The end product is the formation of aldehyde epoxide and peroxide.

8. Example of oxidative rancidity

9. 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. 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 (8 th Edition) Principles of biochemistry (4 th Edition)

26. Thank You 