Transcript Meat Proteins

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 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 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
actin
troponin
tropomyosin
~55%
40 - 45%
desmin, synemin,  actinin, nebulin
and numerous structural proteins
1 -5%
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
old beef
4.0-10.0 mg/g
15.0-20.0 mg/g
mechanically separated
meat
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
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
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
light
Fe
Fe++ + NO
+O2
NO2- (nitrite)
NO
NO2 (nitrogen dioxide gas)
–therefore vacuum systems and vacuum packaging
are essential
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
– 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 NO2but
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.)