Enzim Alami pada Daging

1. Enzim Alami pada Daging

2. Natural Enzymes of Meat • Enzim-enzim glikolitik: enzim-enzim yang berperan pada proses glikolisis postmortem. • Enzim-enzim proteolitik: enzim-enzim yang berperan pada pemecahan protein pada proses pelayuan daging.

3. Glycolytic Enzymes • Hexokinase • Phosphoglucose isomerase • Phosphofructokinase • Aldolase • Triosephosphate isomerase • Gliceraldehyde 3-phosphate dehydrogenase • Phosphogliceratekinase • Phospogliceratemutase • Enolase • Piruvatekinase • Lactate dehydrogenase

4. Step 1 • Glucose is phosphorilated by ATP to form a sugar phosphate. • The negative charge of the phosphate prevents passage of the sugar phosphate through the plasma membrane trapping glucose inside the cell.

5. Step 2 • A readily reversible rearrangement of the chemical structure (isomerization) moves the carbonyl oxygen from carbon 1 to carbon 2 forming a ketose from an aldose sugar.

6. Step 3 • The new hydroxyl group on carbon 1 is phosphorilated by ATP, in preparation for the formation of two three-carbon sugar phosphates. • The entry of sugar into glycolysis is controlled at this step, through regulation of the enzim phosphofructokinase.

7. Step 4 • The six-carbon sugar cleaved to produce two three-carbon molecules. • On the glyceraldehyde 3-phosphate can proceed immediately through glycolysis.

8. Step 5 • The other product of Step 4 dihydroxy aceton phosphate is isomerized to form glyceraldehyde 3-phospate.

9. Step 6 • The two molecules of glyceraldehyde 3-phosphate are oxidized. • The energy generation phase of glycolysis begins, as NADH and a new high-energy anhydride linkage to phosphate are formed.

10. Step 7 • The transfer to ADP of the high-energy phosphate group that was generated in Step 6 forms ATP.

11. Step 8 • The remaining phosphate ester linkage in 3-phosphoglycerate, which has relatively low free energy of hydrolysis, is moved from carbon 3 to carbon 2 to form 2-phosphoglycerate.

12. Step 9 • The removal of water from 2-phosphoglycerate creates a high-energy enol phosphate linkage.

13. Step 10 • The transfer to ADP of the high-energy phosphate group that was generated in Step 9 forms ATP , completing glycolysis.

14. Net ATP resulting from glycolysis

15. Glycolytic Enzymes • Laktat dehidrogenase, mengubah piruvat menjadi laktat. • Jumlah laktat yang dihasilkan tergantung dari jumlah cadangan energi (glikogen) pada saat ternak dipotong. • Jumlah laktat yang dihasilkkan akan mempengaruhi pH daging ultimat daging.

16. Postmortem pH Decline • Normal pH decline is a gradual decrease from approximately 7.4 to 5.6 or 5.7 and then ultimately down to 5.2 to 5.7. • pH ranges can be very slow during the first hour and then remain stable at a relatively high level - 6.5 to 6.8. • pH can drop rapidly to around 5.4 to 5.5 in the first hour and ultimately reach a low pH of 5.3 to 5.6.

17. Proteolytic Enzymes • Enzim non lisosomal berfungsi pada proses pemecahan protein miofibril pada periode awal pelayuan, karena pH otot masih tinggi. • Enzim lisosomal berfungsi pada pemecahan protein miofibril lebih lanjut apabila pH daging sudah mencapai aktivitasnya.

19. Proteolytic Enzymes • Cathepsins, which are stored in lysosomes. Calpains work on Z-lines while cathepsins work on actin-myosin bonds. • Calpains, which are stored in the cytosol near Z-lines and require calcium to be activated, • Calpastatin regulates calpains; the higher the calpastatin levels and activity, the less breakdown of myofibrils.

20. Cathepsin • Cathepsins are a class of globular lysosomal proteases. • Cathepsins contain an active-site cysteine residue. • Main physiological role for cathepsins is general protein turnover in the lysosome. • When cathepsins are directed to the outside of the cell, they can degrade proteins in the extracellular matrix.

21. Cathepsin • Cathepsins are a group of enzymes comprising exo- and endo-peptidases. • Cathepsins are categorized into: cysteine (cathepsins B, H, L, X), serine (cathepsin G), and aspartic (cathepsins D, E) peptidase families.

22. Cathepsin • Many research groups have discarded the contribution of cathepsins to meat tenderisation on the basis of a number of observations. Why? • Firstly, there is not large scale actin and myosin degradation in the postmortem conditioning period; these being primary substrates for cathepsins

23. Cathepsin • Secondly, cathepsins are located in the lysosomes and must therefore be released for them to have access to myofibril proteins and to add to meat tenderness. However, low pH levels and high carcass temperature can enhance the disruption of the lysosomal membrane.

24. Cathepsin • Thirdly, there is little association between cathepsins’ activities and the variation in tenderness in meat samples. However, cathepsins B and L activities at 8 h post-mortem have been found to positively correlate with tenderness in beef.

25. Cathepsin • Cathepsin L hydrolyses the largest number of myofibrillar proteins, including troponin T, I and C, nebulin, titin and tropomyosin; which are degraded during the post-mortem conditioning period as well as myosin and actin,

26. Proteasomes • Proteasome is a multicatalytic protease complex involved in the regulation of a number of basic cellular pathways, by their degradation of proteins in the cytosol and nucleus. • Proteasomes are ubiquitously expressed in the body and are abundant in skeletal muscle.

27. Calpains • Calpains are probably the most extensively researched protease family with regard to meat science and it is widely accepted that proteolytic calpain activity does contribute to meat tenderization. • Calpains are a large family of intracellular cysteine proteases.

28. Calpains • Calpains are a superfamily of 14 cysteine proteases. • The system of calpains in a skeletal muscle consists of at least 3 proteases: μ-calpain (I), m-calpain (II) and calpain (III). • Associated with the calpain proteolytic enzyme family is the calpain-specific endogenous inhibitor, calpastatin

29. Non Lysosomal Enzymes • CANP, membebaskan protein jalur z alpha-aktinin, mendegradasi troponin, mendegradasi sedmin dari miofibril, dan mendegradasi protein Z-nin dari jalur z. • Tripsin pada otot halus, mendegradasi alpha-aktinin, aktin, miosin, dan troponin. • Proteinase tiol netral, dan proteinase kimotripsin basa peranannya belum diketahui secara pasti.