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.)