Rancidity testing is crucial in the feed industry to assess the quality and shelf life of products, indicating chemical changes that produce unpleasant odours and tastes in fats due to oxidative or hydrolytic processes. Proper storage and the use of antioxidants are essential to prevent rancidity, which can negatively impact the safety and quality of animal products. Key methods for prevention include using airtight containers, vacuum packing, and refrigeration.

1. Jasmine Juliet
Teaching Assistant
Biochemistry
AC&RI, Madurai

2. • Rancidity testing is essential in the feed
industry, as a key indicator of product
quality and shelf life.
• It is conducted to determine the level of
oxidation in samples of feed or feed
ingredients

3. Rancidity
Rancidity is a chemical change that results in
an unpleasant odour and taste in a fat or oil.
Types of Rancidity
Hydrolytic rancidity
Oxidative rancidity.

4. 1. Oil becomes rancid due to the decomposition
of fats it contains
2. Milk turns rancid due to not heating it in the
humid atmosphere.
3. Butter changes its smell and taste when it is
kept in an open atmosphere for a longer
duration.

5. Types - Hydrolytic rancidity
Hydrolytic rancidity develops due to the presence
of moisture and by growth of microorganisms
in the fat.
 The microorganisms secrete lipases which split
the triglycerides into glycerol and fatty acids.
 Hydrolytic rancidity of butter releases volatile
butyric acid which gives the bad odour and
taste.

6. Hydrolytic rancidity

8. Types - Oxidative rancidity
Oxidative rancidity occurs in oils and fats
containing unsaturated fatty acids due to
exposure to air.
Unsaturated fatty acids are converted into
hydroperoxides, which break down into
volatile aldehydes, esters, alcohols, ketones,
and hydrocarbons, some of which have
disagreeable odours.

9. Oxidative rancidity

10. Types - Oxidative rancidity
• Fats contaminated with enzymes like lipase undergo
partial hydrolysis and oxidation of unsaturated fatty
acids at the double bonds.
• This is even brought about by the atmospheric moisture
and temperature. Due to this, there is release of
hydrogen peroxide giving a bad odour and taste to the
fat.
• Rancidity can be prevented by antioxidants like
vitamin E, vitamin C, phenols, hydroquinone’s, etc.

12. • Rancidity Process: Rancidity happens in food products
that have oil and fatty acids in them. Any substance
turns rancid in basically three steps:
I. Initiation Reaction: Initiation reaction leads to the
formation of radicals on the food substances because
of external factors like heat and air that stimulates
this reaction. A radical is an atom molecule or ion that
has an unpaired electron. These unpaired electrons
make radicals very reactive chemical substances.
RH ⇒ R- + H+

13. II. Propagation Reaction: In this step, oxygen
present in the atmosphere gives rise to
peroxides. These peroxides react further with
unsaturated fatty acids and then produce new
radicals.
R- + O2 ⇒ ROO- (peroxide)

14. III. Termination Reaction: In the third stage, two
radicals combine together to form a new single
bond.
ROO- + ROO- ⇒ End Products
• Fats, Lipids and other compounds are decomposed
at the end of the rancidification. The process leads to
the formation of highly reactive molecules. Thus,
food starts smelling unpleasant and tastes bad after
rancidity.

16. • There are many possible ways to prevent Rancidity.
Some of them are:
1. Antioxidants (tocopherols, rosemary extract, ascorbyl
palmitate) can be added to foods that contain oils and fats to
slow down oxidative deterioration.
2. To slow down the process of rancidification, food can be
stored in airtight containers.
3. Vacuum packing can be done to keep oxygen out.

17. 4. By adding inert gas such as nitrogen to the bag to
replace oxygen.
5. Food items can be kept in the refrigerator. It will
reduce the rate of most reactions that take part in
rancidity.
6. By storing food in dark places.

19. • Rancidity is a common problem in rendered animal products.
It can have detrimental effects on both the quality and safety
of the product.
• It is caused by the oxidation of fats and oils, leading to the
formation of harmful compounds such as free radicals and
hydroperoxides.
• The best way to prevent rancidity is through proper storage,
packaging, and handling techniques, as well as the use
of antioxidants to slow down the oxidation process. It is
important for manufacturers and consumers to be aware of the
potential for rancidity in rendered animal products and take
the necessary precautions to ensure the safety and quality of
the product.