meat proteins 3 categories 1. myofibrillar (contractile) ~ 55% of total muscle protein but 70-80%+...
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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 = 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 propertiesi.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%
40 - 45%
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)
~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
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 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 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
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 5th bond from iron
– 6th 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 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
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
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 O2 CO2 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, 0oC --- 5 days
– pH 5, 25oC --- 3 hours
– pH 9, 25oC --- 7 days
– pH 9, 0oC --- ~ 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 - 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
To maximize cured color
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
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
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
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 (H2O2)
– 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
– pHphosphates will slow color formation
– heating ratetoo fast will not allow adequate development
– too low nitrite concentration
– too low reductant level (ascorbate, erythorbate)
5. Smoke color variation
– Surface moisture is criticalwet - 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 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.)