Meat Proteins

1. Meat Proteins 3 categories 1. myofibrillar (contractile) ~ 55% of total muscle protein but 70-80%+ of WHC and binding properties • salt soluble with ionic strength of over 0.3 neededµ =  i c2 i = concentrationc = charge • 4% - 5% is best (6 - 8% brine) • brine strength = ___salt___ salt + water • often manipulate brine strength by chopping/mixing all the salt with part of the meat or vice versa. • May use preblends (meat, salt, nitrite) to increase protein solubilized

2. 1. myofibrillar (contractile) • absolutely critical to processing properties i.e.bind values (WHC, fat binding, etc.) • emulsion/batter products such as frankfurters - will cover later • heat-set gelation which controls binding and texture • hams, emulsion/batters, all cooked products

3. 1. myofibrillar proteins are composed of: myosin ~55% actin troponin 40 - 45% tropomyosin desmin, synemin,  actinin, nebulin and numerous structural proteins 1 -5%

4. Myosin is generally considered the singly most important because: • Long filamentous molecule (similar to a 1 inch garden hose that is 8 feet long) • amino acid composition gives highly-charged, polar molecule • present in large quantity in lean muscle

5. Other proteins are also important • Many are charged, polar molecules • structural proteins can have a large influence on “release” of myosin/actin and “opening” protein structure to water. i.e. desmin degradation in aging can increase WHC

6. 2. Stromal proteins (connective tissue) ~10 - 15% of total muscle protein • primarily collagen • most abundant protein in animal body (20 -25% of total body protein) - skin, sinews, tendons, etc. • designed to transmit force and hold things together, therefore these proteins are generally tough and inert - also - content will vary according to muscle function • increased crosslinking as animal age increases toughness and a major cause for sausage and ground beef industries

7. 2. Stromal proteins (connective tissue) • Not very valuable in processed meats --- has little binding ability • will shrink when heated to 140oF+ (with moisture) and convert to gelatin at 160oF - 180oF - but - if heated when dry --- collagen becomes very hard and impermeable --- important to handling of collagen and/or naturalcasings • collagen is highly resistant to enzymes so enzyme tenderizers are generally ineffective

8. 2. Stromal proteins (connective tissue) • Unique protein with ~ 33% glycine and ~10% hydroxyproline therefore very nonpolar noncharged molecules - isoelectric point is about pH 7.2 • by far the only protein to contain large amounts of hydroxyproline - therefore -hydroxyproline measurement is the most common method used to determine collagen content in meat

9. 2. Stromal proteins (connective tissue) • Collagen is used to make gelatin, contact lenses, pharmaceuticals, etc. - and - regenerated sausage casings

11. 2. Stromal proteins (connective tissue) • generally considered a problem in processed meats and high collagen meats often limited to 15 - 25% maximum - however - chopped, ground, powdered collagen which can be dispersed, can be useful in forming a gel when heated and also in retaining water and fat

12. 3. Sarcoplasmic proteins (water soluble, intracellular fluid) ~ 30% of total muscle protein (~ 20% of binding ability) • isoelectric points generally between pH 6 - pH 7 • hundreds of enzymes in cells for energy, growth, etc. • most are relatively low molecular weight (small) proteins

13. Importance of sarcoplasmic proteins 1. Enzyme activity • calpain - tenderization • postmortem glycolysis • pH change • potential flavor contributions from protein hydrolysis  hydrolized proteins 2. Color • myoglobin • responsible for all meat color variations so a good understanding is critical in meat processing

14. Myoglobin • “conjugated” protein • consists of a typical amino acid protein chain - and -a non-protein heme molecule

17. Heme portion • Responsible for all color Protein portion • colorless - but - is important to heme stability and affects color indirectly • free heme oxidizes to brown quickly

18. Heme is attached to the protein by a histidine amino acid and the 5th bond from iron • 6th bond is relatively free to bind oxygen, nitric oxide, carbon monoxide or other compounds that affect color

19. A second histidine on the protein chain --- on the other side of the heme is important to stability of fresh meat color (myoglobin “cleft”) • Not important to cured color

21. So --- what controls meat color? 1. Myoglobin concentration • color intensity poultry white muscle .05 mg/g chicken thigh 1.8-2.0 mg/g turkey thigh 2.5-3.0 mg/g pork, veal 1.0-3.0 mg/g beef 4.0-10.0 mg/g old beef 15.0-20.0 mg/g mechanically separatedmeat 0.08-3.0 mg/g

22. 2. Chemistry • Fresh meat color comes from • myoglobin - Fe++ - no ligand? (purple) • oxymyoglobin - Fe++ - oxygen attached at 6th position on heme (cherry red) • carboxymyoglobin - Fe++ – carbon monoxide at 6th position (cherry red) • metmyoglobin - Fe+++ - no ligand (brown) therefore: oxidation state of Fe(+2,+3) and attached ligand (O2, CO, NO, etc.) determine color

23. Four major chemical factors that affect the pigment forms in fresh meat --- Fresh color - 1. Postmortem age/freshness • myoglobin was biologically designed to hold oxygen, then release it for energy metabolism So - myoglobin binds oxygen somewhat temporarily --- but must be in reduced Fe++ to do that

24. Reducing capacity of muscle keeps iron converted from Fe+++ to Fe++ and improves fresh color. --- depends on active reducing enzymes • Fresh meat is alive uses O2 CO2 to gain some energy to keep enzymes and reducing ability active

25. As long as meat is fresh enough to keep Fe++ reduced, color is desirable (purple red) • With age, reducing capacity is lost and metmyoglobin (brown) begins to predominate

26. 2. pH • High pH favors pigment reduction and fresh color stability • pH is very interactive with and dependent on…..

27. 3. temperature • Lower temperature is better Example: a study of oxymyoglobin half-life (time required to lose 1/2 of the oxymyoglobin present) in solution gave the following --- • pH 5, 0oC --- 5 days • pH 5, 25oC --- 3 hours • pH 9, 25oC --- 7 days • pH 9, 0oC --- ~ 12 months

28. pH is also a factor in cooked color and can affect visual appearance of doneness • High pH • retains pink/red color at high temperatures “pinking” of cooked products • low pH • may result in browning at low temperatures that are microbiologically unsafe “premature browning”

29. 4. Oxygen pressure • atmospheric oxygen pressure gives oxygen binding by myoglobin and red “bloom” from oxygenation of pigment • low oxygen pressure results in oxidation of pigment to metmyoglobin • thus a poor vacuum package can result in discoloration of fresh meat • gives color gradient from surface to inside on fresh meat

32. Oxidation is also accelerated by salt --- • May cause disruption of protein and destabilizing the heme/histidine arrangement • may suppress reducing enzymes • will also result in rancid off-flavors if not compensated correctly

33. Factors controlling cured color • Must attach nitric oxide (NO) to heme to achieve cured color • affinity of NO for heme is ~ 100 times as great as is oxygen therefore NO will react with reduced or oxidized heme • key to cured meat color is formation of NO in meat

35. To maximize cured color 1. Provide sufficient nitrite - NO2- • NO2- + reducing enzymes  NO (relatively slow) • 2 NO2- + 2H+(acid)  2HONO  NO + NO3- +2H+ • NO2- + Fe++ (heme)  Fe+++ + NO these are three natural reactions of nitrite in meat that are significant sources of NO for color development

36. 2. Accelerate NO production from NO2- • increase acidity (H+) • pH of 5.4 will develop cured color twice as fast as pH 5.7 --- may add acid (sodium acid pyrophoshate, glucono delta lactone, citric acid) • increase reducing capacity • add sodium erythorbate or sodium ascorbate • permitted as curing accelerators

37. 3. Heating / cooking • Cured pigment is stabilized by heating over ~ 130oF - 140oF • believed to remove heme from protein chain --- giving free heme and attaches a second NO group to the heme --- resulting in two attached NO groups on either side of the heme

39. Cured meat color will fade Especially in presence of light and oxygen NO Fe Fe++ + NO NO2- (nitrite) +O2 NO NO2 (nitrogen dioxide gas) • therefore vacuum systems and vacuum packaging are essential light

40. Common color problems / questions 1. Iridescent blue-green sheen on roast beef and ham slices • microbiological (hydrogen peroxide) or chemical (nitrite burn, sanitizers) --- least likely • surface fat/oil film --- unlikely • irregular muscle fiber surface from non-perpendicular slicing angle

41. 2. Pigment oxidation - gray, green etc. • Light, oxygen exposure for cured meat • nitrite “burn” - due to abnormally high nitrite concentration • bacterial - some produce hydrogen peroxide (H2O2) • rancid fat - radicals may oxidize heme • close relationship between rancidity and color because oxidized heme iron can induce rancidity

42. 3. Pinking in uncured meat • high pH • nitrite, nitrate contamination from water, vegetables, etc. • carbon monoxide in the environment • transportation truck exhaust • nitrogen oxide gases from cooking • i.e. Hickory Park

43. 4. Poor cured color development • pH phosphates will slow color formation • heating rate too fast will not allow adequate development • too low nitrite concentration • too low reductant level (ascorbate, erythorbate)

44. 5. Smoke color variation • Surface moisture is critical wet - streaked, uneven, - even black if very excessive dry - little or no color

45. 6. Browning of fresh sausage • Salt favors oxidation encapsulated salt • meat freshness is important pre-rigor meat has best color

46. For cured color • Maximize production of NO from NO2- but need to retain a small amount of NO2-(~ 10-20 ppm) in the product for color stability during distribution and display (especially retail lighting in cases, etc.)