Applied Fish Biochemistry

1. SUBMITTED TO:
Dr. Supratim Chowdhury
Dept. of Fish Processing Technology
“Fatty acid composition of fish liver and body oils”
FPT-504
SUBMITTED BY:
Asik Ikbal, M.F.Sc. 1st year 1st sem.
A Seminar on

2. Auto-oxidation of
fatty acids
Rancidity
Lipases and
phospholipases
Pro- and anti-
oxidants Oxidation
indices
Lipid protein
interactions and their
impact on quality

3. • Fish fat is different from both vegetable and animal fats in their fatty acids
make up.
• Animal fats contain mainly saturated fatty acids. Vegetable fats may contain
more unsaturated fatty acids than fish fats.
• However the degree of unsaturation is greater in fish fat than in vegetable fat.
• In human nutrition some fatty acids like linoleic or linolenic acid are regarded as
essential fatty acids(EFA) as they cannot synthesized in body. In fish EFA
constitutes only around 2% of total lipid.

4. • Fish oils are two types-- 1. Body oil 2. Liver oil
• BODY OIL-It is used as industrial oil, while the latter finds application
in pharmaceutical preparations. In India the main source of fish
body oil is the oil sardine.
• LIVER OIL- The high liver lipid content (which can exceeds 50% of
wet weight) of species in family Gadidae, such as cod, Pollock or
haddock, is exploited to produce cod lever oil, a rich source of
omega-3 poly unsaturated fatty acid as well as vitamin A & D.
BEFORE MOVING TO
THE TOPIC
Fish oil

5. Conted….
• Fish oils and marine-animal oils are generally characterized by a rather
large group of saturated and unsaturated fatty acids, which are
commonly associated with mixed triglycerides.
• The fatty acids derived from fish oils are of three principal types:
saturated, monounsaturated, and polyunsaturated.
• The saturated type are Butyric acid, Lauric acid, Myristic acid,Palmitic
acid, Stearic acid.
• The monounsaturated type is comprised of monoethenoic acids
(Palmitoleic acid, Oleic acid), and the polyunsaturated type is comprised
of polyethenoic acids (Eicosapentaenoic acid, Docosahexaenoic acid,
Linoleic acid).

6. Fish oils, as well as other edible oils and fats, if condition is
favourable, spontaneously oxidize in the presence of
atmospheric oxygen or enzymes, at or near the ordinary
temperature. This type of oxidation is called as autoxidation.
• Mechanism of Autoxidation
Chain initiation Propagation Termination

7. Chain initiation
This involves the production of free radicals R or RO2 by the removal
of a hydrogen atom from the alpha methyl group as follows, followed
by the addition of a molecule of O2.
- CH2 – CH = CH – (RHO) CH – CH = CH – (R) - CH – CH = CH – (RO2)
O

8. Propagation
The production of hydroperoxides takes place in the propagation sequence of
reactions. In these reactions, the free radical (R) reacts with O2 to give a peroxide
radical (RO2), which in turn reacts with another substrate, RH to give a
hydroperoxide and another free radical (R) which can initiate the chain of events
again.
R + O2 RO2 RO2+ RH RO2H + R

9. Termination
2R
R+ RO2
Here the peroxides decomposes or react with one another or one other oxidation
products resulting in the formation of non- propagating products like carboxylic acids,
carbonyl compounds and condensation products. These end products are responsible for
the rancid odour and flavor.
Non-propagating
products2RO2

11. What is rancidity?
Rancidity is a very general term and in its most general
meaning, it refers to the spoilage of a food in such a way that
it becomes undesirable (and usually unsafe) for consumption.
Lipid oxidation is one of the major reasons that foods
deteriorate and is caused by the reaction of fats and oils with
molecular oxygen leading to off-flavours that are generally
called rancidity.

12. Types of rancidity
Hydrolytic rancidity:
Hydrolytic rancidity refers to the odour that develops when
triglycerides are hydrolysed and free fatty acids are released. This
reaction of lipid with water sometimes requires a catalyst, but
results in the formation of free fatty acids and salts of free fatty
acids.
Oxidative rancidity :
Oxidative rancidity is associated with the degradation by oxygen
in the air. This is a free radical process, the double bonds of an
unsaturated fatty acid can undergo cleavage, releasing volatile
aldehydes and ketones. Oxidation primarily occurs with
unsaturated fats. For example, even though meat is held under
refrigeration or in a frozen state, the poly unsaturated fat will
continue to oxidize and slowly become rancid.
Microbial rancidity:
Microbial rancidity refers to a process in which microorganisms,
such as bacteria or molds, use their enzymes such as lipases to
break down fat.

13. • The most common enzymes in meat are lipase.
• Lipase is lipid hydrolysing enzyme placed in the lysosome of a cell
and is secreted by micro organisms.
• It digests complex fat (or lipid) molecules into simple, soluble fatty
acid and glycerol molecules. This process called lipolysis. Lipolysed
fats smells and taste rancid and this particular smell and taste
origin from low molecular weight fatty acid such as butyric acid.
• Lipase is deactivated at 72 ̊C. In certain cases a temperature of 80-
82 ̊̊C in necessary to deactivate this enzyme totally.

14. A phospholipase is an enzyme that hydrolyzes phospholipids into
fatty acids and other lipophilic substances. There are four major
classes, termed A, B, C and D, distinguished by the type of reaction
which they catalyze:

15. Contd…..
1. Phospholipase A
Phospholipase A1 - cleaves the SN-1 acyl chain.
Phospholipase A2 - cleaves the SN-2 acyl chain, releasing arachidonic acid.
2. Phospholipase B - cleaves both SN-1 and SN-2 acyl chains; this enzyme is
also known as a lysophospholipase.
3. Phospholipase C- cleaves before the phosphate, releasing diacylglycerol
and a phosphatecontaining head group. Phospholipase Cs play a central
role in signal transduction, releasing the second messenger inositol
triphosphate.
4. Phospholipase D - cleaves after the phosphate, releasing phosphatidic
acid, and an alcohol. Types C and D are considered phosphodiesterases.

16. • Pro-oxidants are chemicals that induce oxidative stress, either by generating
reactive oxygen species or by inhibiting antioxidants systems.
• The oxidative stress produced by these chemicals can damage cells and
tissue. Some substances can serve as either antioxidants or pro-oxidants
depending on conditions.
• Even if these pro –oxidants are originally not present in oils, they are
frequently formed spontaneously during the storage of the oils.
• Besides ascorbate, medically important conditional pro-oxidants include uric
acid and sulfhydryl amino acids such as homocysteine. Typically, this involves
some transition-series metal such as copper or iron as catalyst.

17. • An oxidant is a molecule that inhibits the oxidation of other molecules.
• Oxidation is a chemical reaction that transfer electrons or hydrogen from a substance to an oxidizing
agent.
• Oxidation reactions can produce free radicals.
• In turn, these radicals can start chain reactions.
• When the chain reaction occurs in a cell, it can cause damage or death to the cell.
• Antioxidants terminate these chain reaction by removing free radical intermediates, and inhibit other
oxidation reactions. Antioxidants break the reaction chains by being themselves oxidized, as follows:
ROO. + AH2 ROOH + AH. (Primary attack)
2AH AH2 + A
OR
ROO. + AH. ROOH + A

18. Contd…..
• Antioxidants naturally occur in small concentration in oils and most of them are
phenolic compounds.
• The well known natural antioxidants is tocopherols, occur in small concentration
in arious fish oils in range of 40-628mg/kg of oil.
• Commercially used antioxidants are Butylated hydroxyl anisole (BHA), Butylated
hydroxyl toluene (BHT), Propylgallate, Isoamylagallate, Nordihydroguaiaretic
acid (NDGA) And Resin guaiac.

19. 1. Peroxide value (PV): One of the first tests devised to measure oxidative rancidity
was the peroxide value which measures the peroxides-the intermediates of lipid auto
oxidation. The peroxide value is defined as the amount of peroxide oxygen per 1
kilogram of fat or oil. Traditionally this was expressed in units of mili equivalents,
although if we are using SI units then the appropriate option would be in mili moles
per kilogram.
2. TBA value: This value co relates more closely than peroxide value with sensory
measurement of oxidative rancidity. This test is based on the reaction between
malonaldehyde and 2-thiobarbituric acid to produce pink colour.

20. • Protein–lipid interaction is the influence of membrane proteins on
the lipid physical state or vice versa.
• Intrinsic membrane proteins are solvated by a shell of lipid molecules
interacting with the membrane-penetrating surface of the protein;
these lipid molecules are referred to as annular lipids. Lipid
molecules are also found bound between transmembrane α-helices;
these are referred to as non-annular lipids.
• Annular lipid binding constants depend on fatty acyl chain length, but
the dependence is less than expected from models based on
distortion of the lipid bilayer alone.

21. • This interaction may imply either the formation of physical complexes between
the oxidized lipids and the protein or the formation of various types of covalent
bonds, in addition to the production of protein radicals.
• Those originating from oxidation of the lipid substrate can influence reaction
rates and produce significant consequences in the colour, flavour and texture of
foods.
• Particularly, the reaction of lipid oxidation products with amines, amino acids
and proteins has long been related to both the browning observed in many fatty
foods during processing and storage known to occur during non-enzymatic
browning.
• The rancid flavour that occurs in oils is due to the decomposition of lipid
hydroperoxides to produce aldehydes and ketones.

22. Knowledge of the chemical nature of fish-oil fatty acids and their
distribution in marine life is important for the development of fishery
products and for the evaluation of the nutritional significance of fatty
acids in fish oils.
Knowledge of the distribution of fatty acids is also important in order
to understand the physical and chemical properties of fish oils and the
biochemical role of fatty acids in fish and marine animals.

23. https://en.wikipedia.org/
https://Post Harvest technology of fish and fish products
 - K. K. Balachandran
https:// www.slideshare.net
http://www.fao.org/Chapter 4. Lipids and Fatty Acids