Meat Proteins

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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 to increase protein solubilized

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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

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1. myofibrillar proteins are composed of
myosin 55
actin
40 - 45
troponin
tropomyosin

desmin, synemin, ? actinin, nebulin and numerous
structural proteins
1 -5
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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

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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

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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

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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

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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

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2. Stromal proteins (connective tissue)

• Collagen is used to make gelatin, contact lenses,
  pharmaceuticals, etc.
• - and - regenerated sausage casings

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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

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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

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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

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Myoglobin

• conjugated protein
• consists of a typical amino acid protein chain
• - and -a non-protein heme molecule

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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

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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

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A second histidine on the protein chain --- on
the other side of the heme is important to
stability of fresh meat color.

• Not important to cured color

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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

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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, etc.) determine color

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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

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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

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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

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2. pH

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

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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

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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

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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

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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

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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

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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

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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

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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

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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
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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

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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

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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

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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)

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5. Smoke color variation

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

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6. Browning of fresh sausage

• Salt favors oxidation
• encapsulated salt
• meat freshness is important
• pre-rigor meat has best color

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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.)

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