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 needed µ =  i c 2 i = concentration c = 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

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

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

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

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

2. Stromal proteins (connective tissue) ~ % 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

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

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

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

2. Stromal proteins (connective tissue) –generally considered a problem in processed meats and high collagen meats often limited to % 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

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

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

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

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

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

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

So --- what controls meat color? 1. Myoglobin concentration –color intensity poultry white muscle.05 mg/g chicken thigh mg/g turkey thigh mg/g pork, veal mg/g beef mg/g old beef mg/g mechanically separated meat mg/g

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

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

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 O 2  CO 2 to gain some energy to keep enzymes and reducing ability active

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

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

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, 0 o C days –pH 5, 25 o C hours –pH 9, 25 o C days –pH 9, 0 o C --- ~ 12 months

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”

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

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

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

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

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

3. Heating / cooking –Cured pigment is stabilized by heating over ~ 130 o F o F –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

Cured meat color will fade Especially in presence of light and oxygen NO Fe Fe ++ + NO NO 2 - (nitrite) +O 2 NO NO 2 (nitrogen dioxide gas) –therefore vacuum systems and vacuum packaging are essential light

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

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 (H 2 O 2) –rancid fat - radicals may oxidize heme –close relationship between rancidity and color because oxidized heme iron can induce rancidity

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

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)

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

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

For cured color –Maximize production of NO from NO 2 - but need to retain a small amount of NO 2 - (~ ppm) in the product for color stability during distribution and display (especially retail lighting in cases, etc.)