Fish protein and its functional properties

1. PROTEINS AND CHANGES IN
THE QUALITY OF PROTEINS
DURING DIFFERENT
PROCESSING METHODS
Submitted By
Pooja Saklani

2. INTRODUCTION
 A protein is a polymer consisting of several amino
acids(a polypeptide).
 Each amino acid can be thought of a single carbon
atom(the α carbon) to which there is attached one
carboxyl group, one amino group, and a side chain
denote R.
 The side chains are generally carbon chains or rings
to which various functional groups are attached.
 There are mainly 20 different amino acids present in
nature.

3.  In protein molecules the amino acid residues are
covalently linked to form very long chains. They are
united in a head-to-tail arrangement through
substituted amide linkages called Peptide bond that
arise by elimination of the elements of water from the
carboxyl group of one amino acid and α-amino group of
the next.
 Three amino acids can be joined by two peptide bonds
to form a tripeptide; similarly, amino acids can be linked
to form tetrapeptides ,pentapeptides, and so forth.

4. STRUCTURE OF AMINO ACIDS
 When a few amino acids are joined in this fashion,
the structure is called an oligopeptide.
 When many amino acids are joined, the product is
called a polypeptide.

5. In a peptide, the amino acid residue at the end with a
free -amino group is the amino-terminal (or N-terminal)
residue; the residue at the other end, which has a free
carboxyl group, is the carboxyl-terminal (C-terminal)
residue.

6. CLASSIFICATION OF PROTEIN ON THE BASIS OF R –GROUP
NONPOLAR,ALIPHATIC R-GROUP

7. AROMATIC R-GROUP

8. POLAR, UNCHARGED R-GROUP

9. POSITIVE CHARGED R-GROUP

11.  Some other uncommon amino acids also found in
nature like 4-hydroxyproline, a derivative of proline,
and 5-hydroxylysine, derived from lysine and both are
found in collagen, a fibrous protein of connective
tissues.
 6-N methyl lysine is a constituent of myosin, a
contractile protein of muscle.
• Another important uncommon amino acid is -
carboxyglutamate, found in the bloodclotting protein
prothrombin.
 Selenocysteine it contains selenium rather than the
sulfur of cysteine. Actually derived from serine,
selenocysteine is a constituent of just a few known
proteins.

12.  At pH 7,all amino acids are zwitterionic having
positively charged amino group and a negatively
charged carbooxylate group hence amino acids.

13. PROTEIN COMPOSITION OF FISH-
 The protein of fish muscle tissue can be divided into the
following three group based on solubility.
 Myofibrillar protein
 Sarcoplasmic protein
 Stroma protein
 A similar composition is found in fish and livestock
meat.
 The live stock meat contains more stroma than fish
meat.

14. Myofibrillar Protein-
 Myofibrillar protein is the protein that forms
myofibril, which contains Myosin ,Actin,
Tropomyosin, Troponin and Actinin.
 Myofibrillar protein covers 66-77% of the total
protein in fish meat.
 These proteins are soluble in natural salt solution of
high ionic strength (<0.5)usually ranging from 0.30 to
0.70
 This protein is responsible for coagulation and gel
formation during different processing methods
(mainly in the production of surimi).

15. Myosin-
Myosin is the protein
which forms the thick
filaments .
A molecular weight is
about 500,000 daltons.
It is most abundant
myofibrillar component,
constituting
approximately 40-60%
of total protein content.

16.  Myosin consists of six polypeptide chains and out of
them two heavy chains and four light chains.
 Myosin is a motor molecule that works to move the
cell. This will result in a contraction and expansion
movement.
 Myosin is a special protein that converts adenosine
triphosphate (ATP), a molecule that cells use in order to
live and work, into mechanical energy (energy of work).
This will then generate force and movement.
 Actin,troponin,tropomyosin are thin filaments.

17. Actin-
It constitutes about 22% of the total
myofibrillar protein.
 It can be present as either a free monomer
called G-actin (globular) or as part of a
linear polymer microfilament called F-
actin(filamentous), both of which are essential
for such important cellular functions as the
mobility and contraction of cells during cell
division.

18. Monomer form of actin i.e. G-actin and after
polymerization, actin filaments are formed and called
F- actin.

19. Troponin and Tropomyosin-
 Troponin and tropomyosin regulate muscle contraction.
 Troponin covers 8-10% of total myofibrillar proteins.
 There are 3 type of troponin-
1. Troponin –C (calcium binding)
2. Troponin-I (inhibitory protein)
3. Troponin-T (tropomyosin binding).
 Tropomyosin covers 5-10% of total myofibrillar protein.
 Tropomyosin have two polypeptide alpha and beta
chain and combine to form a tropomyosin dimer.

20. Troponin Tropomyosin

21. Actomyosin-
A complex of actin and myosin of which the
contractile protein filaments of muscle tissue
are composed.
Stroma protein-
 Collagen is the main protein having a structural unit
tropocollagen.
 It having unique amino acid composition,contaning
glycine(33%),proline(12%) and alanin(11%).
 It also contaning a uncommon proteins i.e.
Hydroxyproline(12%) and Hydroxylysine(1%).

22. Sarcoplasmic protein-
 Sarcoplasmic protein contains many kinds of water
soluble proteins (myoalbumin,globulin and enzymes)
called myogen.
 These proteins are soluble in neutral salt solution of low
ionic strength (0.15M).
 It covers a accounts for 25-30% of the total proteins.
 The concentration of sarcoplasmic protein is high in
pelagic fishes such as sardine,mackral while lower in
demersal species.
 The electrophoretic pattern of sarcoplasmic fraction can
be used for species identification.

23. Stroma Protein-
 Stroma proteins accounts for about 3% of total
proteins in teleosts and 10% in elamobraches.
 These are connective tissues and insoluble in neutral
salt solution or in dilute acids or alkalies.
 The component of stroma is collagen, elastin or both.
 Elastin is very resistant to moist heat and cooking.
 Collagen is almost totally insoluble in water or saline
and does not participate in gel formation
 Collagen is present in skin, air bladder of the fish and
it convert in gelatin during heat processing.

24. Functional properties of proteins-
 Protein functionality is defined as those physical and
chemical properties which affect the behavior of protein
in food systems during processing, storage, preparation
and consumption.
 Physicochemical properties that enable proteins to
contribute to the desirable characteristic of food.
 Protein functionality is closely related to physiochemical
and structural characteristics of that protein.
 Functional properties of proteins depends on-
a. size
b. shape
c. amino acid composition and sequence
d. net charge and distribution of charges

25. Some important functions of proteins-
TYPE OF PROTEINS FUNCTIONAL PROPERTIES
a) Biocatalysts Work as enzyme
b) Collagen ,keretin,elastin Structural components of cells and organs
c) Actin, myosin Contractile proteins
d) Insuline, growth factors Hormones
e) Serum albumin, transferrin,
hemoglobin
Work as transport proteins
f) Phosvitin ,ferritin They are metaloproteins
g) Immunoglobulins Act as antibodies
h) Seed proteins casein micelles,egg
albumin
They are work as protective proteins

26.  The main functional quality of protein is Gel Formation-
myofibrillar proteins mainly responsible for it.
 Of the MPs, myosin and actin contribute most of the
development of desirable gel characteristics in processed
meat products. The heat-induced gelation of myosin
results in the formation of a 3-dimensional network
structure that holds water in a less mobile state (Yasui
and others 1979).
 During network formation fat and water retention are
enhanced and these influence the yield, texture, and
cohesion of the final product as well as determine the
gelling capacity of MPs (Smith and others 1988).

27. Factors affecting the gel fomation in MPs-
 Myosin-Myosin can form excellent gels.
 Types of muscles-White muscle generally forms stronger
gels than red muscle.
 Source of muscles-Gel forming ability of muscles from
different species is complex, and is influenced by different
processing conditions. Usually chicken muscle forms
stronger gels than beef. Chicken and pork muscle form gels
with almost the same strength.
 pH- Gelation properties of myofibrillar protein are strongly
pH-dependent. At the isoelectric point of myofibrillar
protein (pH 5.3), either only poor gels are formed or gel
formation is inhibited.

28.  At pH 6, the optimum pH value for heat-induced
gelation of myosin is reached. Myofibrillar protein can
form a gel at lower pH without heating.
 Ionic strength-It is generally accepted that a high
concentration (2- 3%) of sodium chloride is required to
solubilize the MPs to form a good gel.
 Heating rate-A slow heating rate may allow more
favorable protein-protein interactions to occur,
producing a stronger, better-ordered 3-dimensional gel.
 Temperature-The optimal temperature for the heat-
induced gelation of myosin at pH 6 is 60 to 70 °C.

29. The gel forming ability of MPs is responsible for
surimi production.
By the use of surimi we can make many analogue
products.
Main 2 steps taking
place during surimi
production-
• a) Denaturation
• b) Aggregation
Some cryoprotactant
like salt(2%), polyphosphate(2%) and sucrose (4%)
are also used.

30. Solubility-
 Solubility of muscle protein is a function of protein
structure, structure of myofibril, pH and ionic
concentration(Xiong,1997).
 Solubility can be defined as the amount of total protein
that goes into solution under specified condition.
 The solubility of proteins in aqueous buffers depends
on the distribution of hydrophilic and hydrophobic
amino acid residues on the protein’s surface.
 Salting out is an effect based on the hydrophilic and
hydrophobic interaction, in which the hydrophobic
could be less soluble at high salt concentrations.
 It is used as method of separating proteins.
 The salt concentration needed for the protein
to precipitate out of the solution differs from protein to
protein

31. Viscosity-
 The resistance of fluid to flow is measured by their
viscosity(Van Hold,1985).
 Viscosity provides information on physico- chemical
interaction among proteins by indicating structural
changes that may occurs in the proteins molecules
(Kinsella,1976).
 Viscosity has been used to determine the degree of
protein denaturation and aggregation during frozen
storage (Colmenero and Borderias,1983).
 It is considered a more reliable index of fish protein
quality than protein solubility or emulsifying capacity
(Colmenero et al.,1988).

32. Emulsification Properties-
 Formulated meat products have been referred to as
emulsion as they contain water phase, oil phase and an
emulsifier.
 An emulsion is defined as heterogeneous systems
consisting of two immiscible liquid phase one of which is
dispersed and other is droplet(Das,1990).
 The formation of emulsion requires the application of
energy, when energy is applied to water and oil, the
phases may be dispersed(Mangino,1994).
 Proteins by virtue of their structure and conformation act
as excellent emulsifier and reduce their interfacial energy
at oil water interphase. Myosin and actomyosin molecule
are good emulsifiers by virtue of their having hydrophobic
and hydrophilic residues.

33. Factors responsible for change in the quality of proteins-
 There are various factors which are responsible for
the change in the quality of proteins-
a. Temperature
b. pH
c. Salt concentration
d. Acids ,bases ratio
e. Pressure.

34. Denaturation of proteins-
 Denaturation -is a process in which proteins or nucleic
acids lose the quaternary structure, tertiary structure
and secondary structure.
 Which is present in their native state, by application of
some external stress or compound such as a
strong acid or base, a concentrated inorganic salt,
an organic solvent (e.g., alcohol or chloroform), radiation
or heat.
 If proteins in a living cell are denatured, this results in
disruption of cell activity and possibly cell death.
 Denatured proteins can exhibit a wide range of
characteristics, from conformational change and loss of
solubility to aggregation due to the exposure
of hydrophobic groups.

35.  Denaturation of fish proteins during different
procsessing methods (freezing, drying) due to change in
temperature, pH, and acid or base concentration etc.

36. Change in the quality of
protein after cooking-
 Protein goes through certain
chemical changes when it is
heated and cooked. When the
proteins in food are heated, they
coagulate, which means they
become firm.
 When exposed to hot
temperatures, the protein
shrinks and losses moisture. This
usually occurs at temperatures
between 160 and 185˚F.
 When meat sources of protein
are cooked slowly, any
connective tissues are likely to
dissolve. Heat does not destroy
the protein in food, though it
might reduce the overall content
slightly.

37. Effect of pH and salt on protein quality-
 During post mortem changes,there is formation of acids, so
at low pH most of the main muscle proteins are at their
isoelectric point and the meat fails to attract and hold
water, so it releases drip. This phenomenon is known as
“drip loss”.
 Salt (NaCl) is highly water soluble. The functions that salt
provides in meat mixtures are mainly determined by the
dissociated ions Na+ and Cl-. When salt is mixed with
comminuted meat the Cl- ion increases the negative charge
of the proteins. The adsorption of Cl- ions onto the
positively charged groups of myosin results in a shift in its
isoelectric point to a lower pH, also causing a weakening of
the interaction between oppositely charged groups at a pH
greater than the isoelectric point.

38.  In the presence of salt, part of the insoluble myosin
passes into the liquid phase and dissolves, increasing
meat swelling and water holding capacity in its
dissociated ionized form (H+ OH-).
 Salt-solubilized myofibrillar proteins form a sticky
exudate on the surface of the meat pieces, which
binds them together after cooking. This layer forms a
matrix of heat-coagulated protein which entraps free
water. The increased water-holding capacity of salt-
treated meat gives it a higher cooking yield, and
greater tenderness and juiciness when the product is
consumed

39.  Reference-
1. Fish processing technology and product
development (A.S.Ninawe and K.Rathnakumar).
2. Textbook of fish processing technology
(K.Gopakumar).
3. Principle of biochemistry( Lehniger).

40. THANK YOU