Rancidity and hydrolysis

1. Rancidity
• Rancidity is a term generally used to denote
unpleasant odours and flavours in foods
resulting from deterioration in the fat or oil
portion of a food.
• There are two basic types or causes of
rancidity that cause and/or contribute to the
degradation of stored edible oils: oxidative
and hydrolytic

2. Rancidification

3. Types
•Oxidative Rancidity
•Hydrolytic Rancidity
a.Enzymatic Rancidity
b.Microbial rancidity

4. Oxidative rancidity
Autoxidation, occurs
when oxygen is absorbed
from the environment

5. Oxidation of fat
• Oil oxidation is an undesirable series of
chemical reactions involving oxygen that
degrades the quality of an oil.
• Oxidation eventually produces rancidity in oil,
with accompanying off flavours, foul-tasting
and horrible smells.
• All oil is in a state of oxidation - you cannot
stop it completely - but there are ways to
reduce it.

6. Oxidation of fat
• Oxidation of fatty acid alkenes involves
cleavage of the double bonds to form short-
chain carboxylic acids.
• When oil oxidises it produces a series of
breakdown products in stages, starting with
primary oxidation products (peroxides, dienes,
free fatty acids), then secondary products
(carbonyls, aldehydes, trienes) and finally
tertiary products.

8. Auto-oxidation
The process of oxidation induced by air at room
temperature referred to as “autoxidation”.
Oxidation progresses at different rates depending
on factors such as
• Temperature,
• Light,
• Availability of oxygen,
• Presence of moisture and metals (such as iron) .

9. Auto-oxidation
Ordinarily, this is a slow process which occurs
only to a limited degree.
However, factors such as the presence of light
can increase the rate of oxidation.
Metals, such as copper or iron, present at low
levels in fats and oils can also promote
autoxidation.

10. Prevent oxidation
Several different factors can be controlled to reduce the
amount of oxidation that occurs in your oil.
• Temperature - the number one contributing factor of
oxidation in oil. If possible reduce the temperature to
the lowest possible throughout processing, shipping
and manufacture.
• Oxygen exposure (in the air) will be a catalyst for
production of free radicals. To reduce oxidation, seal all
containers with the smallest possible headspace,
reduce the area of the oil in contact with air and/or
cover the oil with an inert gas (like nitrogen) at all
possible points.

11. Prevent oxidation
• Light (UV) can trigger the oxidative
degenerative cascade. Reduce the exposure of
the oil to direct light by using brown
glass/plastic containers or black plastic bags.
• Moisture in combination with these other
factors can accelerate oxidation. If possible
limit the amount of water in the oil to less
than 0.2%.

12. Prevent oxidation
• Transition metals, in particular transition metals
like iron and copper, can act as pro-oxidants.
• Fats and oils are normally treated with chelating
agents such as citric acid to complex these trace
metals (thus inactivating their prooxidant effect).
• If possible, you may need to change equipment
(e.g. no brass valves),
• limit time in contact with and/or
• remove transition metals from the oil to reduce
oxidation.

13. Antioxidants

14. Antioxidants (AOX)
• Antioxidants (AOX) terminate the oxidation
chain reactions and inhibit other oxidation
reactions by being oxidised themselves. AOX
do not stop oxidation, but do slow down the
rate at which oxidation occurs.
• There are many different ways AOX can
reduce oxidation, so it is important to choose
the right AOX for your application/product.
• AOX can be synthetic or extracted from
natural plant sources.

15. Common AOX are:
• Tocopherols (vitamin E)
• Carotenoids β-carotene
• Phospholipids
• Retinol (vitamin A)

16. Synthetic Antioxidant
• BHT- butylated hydroxytoluene
• BHA - butylated hydroxyanisole
• TBHQ - tert-Butylhydroquinone
• Propyl gallate
• Ethoxyquin

17. Natural Antioxidant
• Flavonoids
• Rosemary
• Spice extracts
• Tea
• Catechins
• Seaweed

18. Preventive AOX
• Citric acid,
• Phosphoric acid,
• Ascorbic acid (vitamin C),
• Ethylene diamine tetraacetic acid (EDTA),
• Uric acid

19. Hydrolysis

20. Hydrolysis
Hydrolytic rancidity, also
called hydrolysis or
enzymatic oxidation, occurs
in the absence of air, but
with moisture present.

21. Enzyme hydrolysis
Enzymes found naturally in plant oils (i.e.,
lipoxygenase, cyclooxygenase) and animal fats
(i.e., lipase) can catalyze reactions between
water and oil

22. Hydrolysis of Glycerides/Fat

23. Microbial rancidity
Microbial rancidity, in which micro-
organisms such as bacteria, molds and
yeast use their enzymes to break down
chemical structures in the oil,
producing unwanted odors and
flavors. Water needs to be present for
microbial growth to occur.