types of enzyme and protein involvement changes in postmortem

2. Enzymes
– Postmortem processes in meat and fish involve
a large number of chemical and biochemical
reactions that are closely related to the
development of colour, flavour and texture.
– Meat and fish are particularly rich in proteins
and lipids, and, thus, biochemical reactions
such as proteolysis and lipolysis are basic for
sensory quality development, especially during
maturation or ageing.

3. Endogenous enzymes in muscle
food
Enzymes
Peptidases
Exopeptidases
Endopeptidases
or proteinases
Lipolytic
enzymes

4. Proteolytic
enzymes
Cathepsins
Carboxypeptidases
Tripeptidylpeptidases
(TPP)
Caspases
Proteasome
Calpains
Arginyl, alanyl,
leucyl, pyroglutamyl
and methionyl
aminopeptidases
Dipeptidylpeptidases
(DPP)
ExopeptidaseEndopeptidase

5. 1.Calpain system
– Calcium activated cysteine protease or calpain system is thought to be
protease primarily responsible for postmortem tenderization.
– Three isoforms have been identified
Calpain 1-μ (micro molecular)
Calpain 2-m (milli molecular)
Calpain 3 association with titin in the myofibrillar structure.
Calpain-m play role in postmortem tenderization.

6. 2. Calpastatin
– It is specific inhibitor of μ- and m-calpain that limits activity.
– Increasing abundance meat tenderness tends to decreases.
– Cattle: Calpastatin level increases tend to tougher the muscle tissue

7. 3.Proteasome and Caspase
– Proteasome is a protease capable of degrading both sarcoplasmic
and myofibrillar proteins into their amino acid components.
– A large molecular mass of about 700 kDa and a cylinder-shaped
structure with several subunits with optimal activity at a pH
of>7.0.
– Caspase enzymes are family of protease that participate in
programmed cellular death and thus immediate postmortem
changes in proteins.

8. Lipolytic enzyme
Lysosomal acid
lipase
Neutral lipase
Lipases
Acid
phospholipase
Hormone-
sensitive lipase

9. Major enzymatic postmortem changes in muscle
foods
– Proteolysis
– Lipolysis
– Nucleotide
degradation
ATP ADP+AMP Inosine monophosphate
ATPase AMP deaminase
ATP: Adenosine triphosphate
ADP: Adenosine diphosphate
AMP: Adenosine monophosphate

10. Main roles of enzymes in the quality
and safety of meat and fish
– Enzymes and flavor
– Enzymes and oxidation
– Enzymes for improved tenderness
– Enzymes and antimicrobial action

11. Proteins
– Major constituents of muscle 20% total
muscle weight or 80% of dry mass in lean
tissue
– Role of protein
EAA and closely resembling to human
body
Specific functionalities (gelation,
emulsification, water-holding
Greatly contribute to texture,
appearance, mouthfeel and juiciness.

12. Muscle Protein
– It can be divided into three types based on
solubility
Sarcoplasmic : 35%
Myofibrillar : 60%
Stromal : 15%

13. 1.Sarcoplasmic protein
– Protein fraction consists of at least 500 individual protein metabolic enzymes.
– It have globular structure with high density polar and charged side chains.
– Myoglobin:
- A 17,000-Da protein, is probably the best-known member in this superfamily
because of its prominent role as the chief pigmentation protein in fresh meat.
- Conjugated protein ( amine and non-protein molecule is heme).

14.  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.

15. Importance of sarcoplasmic
protein
1. Enzymes:
- calpain: tenderization
- postmortem glycolysis
-pH change
- potential contribution to flavor
2. Color:
- myoglobin

16. 2.Myofibrillar proteins
– The most abundant protein fraction that makes up the myofibril
– It is responsible for much of the functional characteristics of fresh and
processed meat.
Myosin and Actin, the two most preponderant constituents in the
myofibril, account for more than 70% of total myofibrillar protein.
– Other proteins present in the myofibrils, including titin and nebulin
(scaffold proteins), tropomyosin, troponins, α-actinin, desmin, C-, M-,
and X-proteins, and many other minor polypeptides

17. 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.

18.  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.

19. 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.

20. – Monomer form of actin i.e. G-actin and after polymerization, actin filament
are formed and called F- actin.

21. – Proteins in myofibril are located within four structural units
Thick filaments : myosin, c-protein, m-protein
Thin filaments : actin, tropomyosin, troponin complex
Cytoskeletal filaments : Titin and Nebulin
Z-disks : alpha actitin, zeugmatin, desmin

22. 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.

23. Troponin
Tropomyosin

24. Actomyosin
– A complex of actin and myosin of which the
contractile protein filaments of muscle tissue are
composed.

25. 3.Stromal Protein
– Soluble only in acid or alkaline solutions
– Referred to as connective tissue proteins
– Connective proteins: collagen, reticulin and elastin
these are extracellular proteins, make up the fine
collagenous and reticular fibrils that are major
constituents
Endomysium: individual muscle fibers
Perimysium: muscle fiber bundles (background for
“toughness of meat”).

26. Collagen
 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.
 Collagen is the main protein having a
structural unit tropocollagen.
 It having unique amino acid composition,
containing Glycine(33%),Proline(12%)
and Alanin(11%).
 It also containing a uncommon
proteins i.e. Hydroxyproline(12%)
and Hydroxylysine(1%).

27. Proteolysis
– An important group of reactions
during meat and fish
processing.
– Proteolysis has a major impact
on texture and thus, the
tendency of postmortem meat
or fish.
– Soften the tissues due to the
breakdown of the myofibrillar
proteins responsible for the
muscle network.

28. Reference
– Rickey Y. Yada., 2004. “Muscle Protein’. Protein in processing. pg.no127-148.
– Rickey Y. Yada., 2015. “Enzymes in meat and fish”. Improving and Tailoring Enzymes
for Food Quality and Functionality. pg.no 199-217.
– Peter P. Purslow., 2017. Muscle Structure, Proteins, and Meat Quality. New Aspects
of Meat Quality. pg.no 13-31.

29. THANK
YOU