Functional Properties of Muscle Proteins in Processed Poultry Products

1. Functional Properties of MuscleProteins in Processed PoultryProducts

2. Functional Properties of Protein • Functional properties are defined as physical or chemical properties of proteins that determine their behavior in foods during processing, storage, and consumption. • Protein functional properties in poultry meat products can be classified into three categories: (1) protein-water interactions, (2) protein-fat interactions, and (3) protein-protein interactions.

3. Factors affecting functional property of Protein • Type of product, • Source of meat, • Type and concentration of non-meat ingredients, • Type of processing equipment used, • Processing conditions, • Stage of processing.

4. Processing conditions • Comminution method • Chopping temperature • Chopping time • Tumbling method • Tumbling time • Tumbling temperature • Pumping and holding

5. Processing conditions • Cooking temperature • Cooking time • Cooking rate

6. Protein functional properties • Protein-Water Interactions • Extractability • Solubility • Water holding • Viscosity • Protein-Fat Interactions • Emulsification • Fat holding • Protein-Protein Interactions • Gelation

7. Ingredients • Source of meat • Salt concentration • Salt type • pH of meat • Moisture content

8. Ingredients • Fat content • Protein content • Other ingredients

9. Product attributes • Textural properties • Organoleptic properties • Appearance • Yield

10. Muscle protein • Poultry meat is comprised of about 20 to 23% protein. • Muscle proteins are divided into three categories based primarily on their solubility properties: myofibrillar, sarcoplasmic, and stromal.

11. Myofibrillar proteins • The myofibrillar or salt-soluble proteins comprise about 50 to 56% of the total skeletal muscle protein. • The proteins are insoluble in water, but most are soluble at salt concentrations above 1%.

12. Myofibrillar proteins • Myofibrils extend the length of a muscle fiber or cell and are surrounded by the sarcoplasm. • Asingle muscle fiber may contain 1000 to 2000 myofibrils.

13. Myofibrillar proteins • Contractile proteins, which are responsible for muscle contraction, • Examples: myosin, actin • Regulatory proteins, involved in regulation and control of contraction, • Examples: tropomyosin, troponin

14. Myofibrillar proteins • Cytoskeletal proteins, that support and maintain the structural integrity of the myofibril. • Examples: titan, nebulin

15. Myosin • Predominant protein in the thick filament of the sarcomere and comprises about 50 to 55% of the total myofibrillar protein. • Myosin is along thin molecule with dimensions of about 150 nm in length by 1.5 nm in width in the rod region and 8 nm in width in the globular head region.

16. Myosin • Poultry skeletal muscle myosin is a large molecule of about 520 kDa and is comprised of 6 polypeptide chains or subunits. • The subunits include two heavy chains of about 222 kDa each and 2 pairs of light chains ranging from 17 to 23 kDa.

17. Actin • Actin is the second most abundant myofibrillar protein and comprises about 20 to 25% of this fraction. • G-actin is a globular protein with a molecular mass of about 42 kDa. • Actin, troponin and tropomyosin, make up the thin filaments of the sarcomere.

18. Actin • Myosin binds reversibly to actin in the thin filaments during muscle contraction. • In post-rigor muscle, the globular head or subfragment-1 region of myosin binds irreversibly to actin to form a complex known as actomyosin.

19. Sarcoplasmic proteins • Sarcoplasmic proteins are located inside the muscle cell membrane in the sarcoplasm and comprise about 30–35% of the total muscle protein.

20. Sarcoplasmic proteins • These proteins are soluble in water or low ionic strength solutions. • Example: Glycolytic enzymes, mitochondrial/ oxidative enzymes, lysosomal enzymes, myoglobin and other heme proteins

21. Stroma proteins • Stroma proteins, often referred to as connective tissue proteins. • Stromaa protein support the muscle structure by surrounding the muscle fibers and entire muscle.

22. Stroma proteins • Connective tissue surrounding the muscle is called epimysium. • Connective tissue surrounding bundles of muscle fibers is called perimysium,

23. Stroma proteins • Connective tissue surrounding individual fibers is called endomysium. • Stroma proteins usually comprise about 3 to 6% of the total protein of poultry skeletal muscle. • The major stroma protein is collagen.

24. Stroma proteins • Elastin and reticulin are minor constituents of the stroma • All of these proteins are insoluble in water and salt solutions. • Meat tenderness often decreases with age of the animal due to the increased cross-linking and other modifications that occur to collagen.

25. Role of proteins in comminuted products • Meat batters are complex systems consisting of solubilized muscle proteins, muscle fibers, fragmented myofibrils, fat cells, fat droplets, water, salts, phosphates, and other ingredients. • Comminuted products, such as frankfurters, bologna and sausages, typically contain about 17 to 20% protein, 0 to 20% fat, and 60 to 80% water.

26. Role of proteins in comminuted products • In meat formulations about 1.5 to 2% salt is typically used to allow for the extraction and solubilization of the myofibrillar proteins. • Comminution refers to as chopping, physically disrupts the muscle tissue by damaging the sarcolema (muscle cell membrane) and the supporting network of connective tissue.

27. Role of proteins in comminuted products • In the presence of salt, the muscle fibers swell, myofibrils are fragmented into shorter pieces, and myofibrillar proteins are extracted and solubilized. • It leads to the formation of a thick, paste-like batter which holds water and stabilizes fat.

28. Role of proteins in comminuted products • Upon cooking, the extracted and solubilized muscle proteins in the batter form a cross-linked gel matrix that binds the water and fat and forms the typical texture associated with cooked comminuted products.

29. Role of proteins in formed products • Formed poultry products are made from chunks or pieces of meat that are bonded or glued together. • Similar events occur during the production of both comminuted products and formed products.

30. Role of proteins in formed products • Tumbling, massaging, or mixing in the presence of salt are used to disrupt the muscle cells, disintegrate the muscle fibers, and extract the myofibrillar proteins from the surface of the meat pieces.

31. Role of proteins in formed products • This extracted protein exudate forms a gel on cooking that acts like a glue to hold the pieces of meat together. • The myofibrillar protein, myosin, is thought to contribute most to the binding strength of the protein exudate. • Collagen has been found to interrupt the binding of the meat pieces when present on the surface.

32. Protein-water interactions • protein extraction and solubilization, • water retention, • viscosity.

33. Protein-water interactions • Protein extractability is a term used to describe the amount of protein that is released or dissociated from the organized myofibrillar structure during processing. • Water retention describes the ability of a protein matrix to retain water or absorb added water in response to an external force, such as during cooking, centrifugation, or pressing.

34. Protein-water interactions • Viscosity, defined by rheologists as the resistance of a material to flow, has a large influence on the stability of the raw product prior to cooking.

35. Effect of salt on protein-water interactions • Water binding increases as the salt concentration is increased. • The addition of salt reduces electrostatic interactions between protein molecules to increase protein extractability, solubility, and water binding.

36. Effect of salt on protein-water interactions • Chopping or tumbling of meat in the presence of salt disrupts the muscle tissue allowing the muscle fibers to absorb water and swell, which leads to an increase in viscosity of the batter.

37. Effect of salt on protein-water interactions • Individual myofibrils are released from the muscle fibers and are fragmented into shorter pieces. • Myosin also bind water and increase the viscosity of a poultry meat batter which helps to stabilize dispersed fat.

38. Effect of salt on protein-water interactions • For these reasons, about 1.5 to 2.0% salt is added to most poultry product formulations.

39. Effect of pH on protein-water interactions • pH of the poultry meat batter also has a large influence on the extractability, solubility and water- • Water binding is lowest at the isoelectric point of myosin and actin (near pH 5.0).binding ability of the muscle proteins.

40. Effect of pH on protein-water interactions • The water-binding ability of the muscle homogenate is increased as the pH is adjusted away from this isoelectric point. • As the pH is increased, the proteins become more negatively charged.

41. Effect of pH on protein-water interactions • As the pH is increased, the extractability and solubility of the myofibrillar proteins are increased as the proteins become more negatively charged. • Alkaline phosphates are commonly used in poultry products.

42. Processing factors affecting protein-water interactions • Time and temperature of chopping of comminuted products and tumbling of formed products must be carefully controlled during processing. • Excessive chopping or tumbling can lead to protein denaturation, usually due to increased temperature.

43. Processing factors affecting protein-water interactions • Denaturation occurs when the native protein structure is destabilized and partially unfolded. • Denatured muscle proteins usually form insoluble aggregates that have poor water-binding and film-forming abilities.

44. Processing factors affecting protein-water interactions • Excessive chopping or tumbling may also lead to excessive disintegration of the muscle fibers and to a reduction in batter viscosity, which reduces the quality of the cooked gel network.

45. Protein-fat interactions • In comminuted products, the fat droplets form the dispersed phase, while the continuous phase is comprised of water, protein, and salt. • At high temperatures and with sufficient energy input, the fat cell membranes are disrupted and the solid fat is melted and emulsified into liquid droplets.

46. Protein-fat interactions • Most poultry fat begins to melt at about 13oC, but due to the variety of lipids present, poultry fat is not completely melted until a temperature of 33oC is reached.

47. Protein-protein interactions • Protein-protein interactions during cooking lead to the formation of a protein gel matrix. • Protein gel is formed during heating when muscle proteins unfold and aggregate to form a continuous, defined solid cross-linked network or matrix.

48. Protein-protein interactions • The formation of a continuous protein gel network has a large influence on the textural and sensory properties, as well as the cooking yields, of poultry products. • The gelation of the myofibrillar proteins occurs during thermal processing of both comminuted and formed products and is probably the most important functional property in processed poultry products during cooking.