Meat Color

Objectives:

(1) To demonstrate the relationship between myoglobin and meat color.

(2) To show how the chemical state of myoglobin is related to meat color.

(3) To identify factors associated with the discoloration of fresh meat.

Reading material: Principles of Meat Science (3rd Edition), chapter 6, pages 126 to 131.


Key terms used to describe color

Hue, chroma, and value

  • Hue – words we normally think of as describing color: red, purple, blue, etc.
  • Chroma – strength or dominance of the hue
  • Value – overall intensity to how light or dark a color is.

L*, a*, b* color space (pronounced “L-star, a-star, b-star”) for instrumental measurements

  • L* – black to white
  • a* – red to green
  • b* – yellow to blue

Heme pigment found in myoglobin

 

Heme pigment

 

Hemoglobin — transports O2 from lungs to cells

Myoglobin — stores O2 in cells

Meat color is impacted by the following factors:

Quantity of myoglobin

Age within species — myoglobin loses its affinity for oxygen as age increases.

Myoglobin differences: Age within species

Age classMyoglobin content
Veal2 mg/g
Calf4 mg/g
Young beef8 mg/g
Old beef18 mg/g

Species differences — age related as well as differences between “red” versus “white” muscle fibers.

Myoglobin differences: Species effects

SpeciesColorMyoglobin content
PorkPink2 mg/g
LambLight red6 mg/g
BeefCherry red8 mg/g

Type of muscle

Myoglobin differences: Muscle effects

MuscleNameMyoglobin content
LocomotiveExtensor carpi radialis12 mg/g
SupportLongissimus dorsi6 mg/g

Chemical state of myoglobin

Chemical state of myoglobin -- Ferrous or Fe++ (covalent bonds)

CompoundColorName
:H2OPurpleDeoxymyoglobin
:O2RedOxymyoglobin
:NOCured pinkNitric oxide myoglobin
:CORedCarboxymyoglobin

Chemical state of myoglobin -- Ferric or Fe+++ (ionic bonds)

CompoundColorName
-CNRedCyanmetmyoglobin
-OHBrownMetmyoglobin
-SHGreenSulfmyoglobin
-H2O2GreenCholeglobin

 

Meat color triangle

Mancini, R. A., and M. C. Hunt. 2005. Current research in meat color. Meat Sci. 71:100-121. doi: 10.1016/j.meatsci.2005.03.003

Metmyoglobin Reducing Activity (MRA)

The system in muscle that converts metmyoglobin back into deoxymyoglobin (without oxygen) and oxymyoglobin (with oxygen) through a series of reactions until the reductants are depleted.

High MRA = M. longissimus lumborum

Low MRA = M. psoas major

Oxygen Consumption Rate (OCR)

The respiration rate of muscles over time during display, which competes with the myoglobin for enough oxygen to keep the muscle in the oxymyoglobin state.

High OCR = M. psoas major

Low OCR = M. gluteus medius

Color stability varies across muscles

Color stabilityMuscle
"High" color stabilityM. longissimus lumborum
M. longissimus thoracis
M. semitendinosus
M. tensor fasciae latae
"Moderate" color stabilityM. semimembranosus
M. rectus femoris
M. vastus lateralis
"Intermediate" color stabilityM. trapezius
M. gluteus medius
M. latissimus dorsi
"Low" color stabilityM. triceps brachii – long head
M. gluteobiceps (M. biceps femoris)
M. pectoralis profundus
M. adductor
M. triceps brachii – lateral head
M. serratus ventralis
"Very low" color stabilityM. supraspinatus
M. infraspinatus
M. psoas major

Source: McKenna, D. R., P. D. Mies, B. E. Baird, K. D. Pfeiffer, J. W. Ellebracht, and J. W. Savell. 2005. Biochemical and physical factors affecting discoloration characteristics of 19 bovine muscles. Meat Sci. 70:665-682. doi:10.1016/j.meatsci.2005.02.016

Two meat color problems with cooked ground beef

Premature Browning
  • Usually caused by highly oxidized meat or meat that is exposed to high-oxygen atmospheres
  • Meat will turn brown around 130°F internal temperature
  • Reason why color is not a good indicator of cooked meat
Persistent Pinkness
  • Usually caused by high pH meat
  • Product will stay pink (uncooked color) even with degrees of doneness that should ensure appropriate cooked endpoint are followed.

Vitamin E feeding of cattle

Vitamin E can be fed to livestock to increase the alpha-tocopherol concentration in muscle. Alpha-tocopherol is an antioxidant and retards the conversion of deoxymyoglobin and oxymyoglobin to metmyoglobin.

Activity of bacteria

PigmentCatalystNew pigment
OxymyoglobinOxidation + bacteriaMetmyoglobin (-OH)
MetmyoglobinBacteriaCholeglobin (-H2O2
MetmyoglobinBacteriaSulfmyoglobin (-SH)

Curing

Myoglobin
Oxymyoglobin
Metmyoglobin
Plus NONitric oxide myoglobinPlus heatNitrosyl hemochromogen

Wrapping film

Vacuum packages (polyvinylidene chloride-polyvinyl chloride); barrier to O2

Retail film (polyvinyl chloride); permeable to O2


Review of Material — What the student should know:

(1) What causes meat to have a particular color.

(2) The role of bacteria in color development and maintenance.

(3) The influence of oxygen on meat color.

(4) The chemistry behind myoglobin and meat color.


Links to related sites

 

J.W. Savell, revised October, 2020

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