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.


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:

(1) Quantity of myoglobin

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

Age class Myoglobin content
Veal 2 mg/g
Calf 4 mg/g
Young beef 8 mg/g
Old beef 18 mg/g

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

Species Color Myoglobin content
Pork Pink 2 mg/g
Lamb Light red 6 mg/g
Beef Cherry red 8 mg/g

(c) Type of muscle

 

Type of muscle Name Myoglobin content
Locomotive Extensor carpi radialis 12 mg/g
Support Longissimus dorsi 6 mg/g

 

(2) Chemical state of myoglobin

Bonds Compound Color Name
Fe++ Ferrous (covalent) :H2O Purple Reduced myoglobin
:O2 Red Oxymyoglobin
:NO Cured pink Nitric oxide myoglobin
:CO Red Carboxymyoglobin
Fe+++ Ferric (ionic) -CN Red Cyanmetmyoglobin
-OH Brown Metmyoglobin
-SH Green Sulfmyoglobin
-H2O2 Green Choleglobin

 

 

Color flow chart

(3) Metmyoglobin Reducing Activity (MRA)

reduced myoglobin —> oxymyoglobin —> metmyoglobin —> reduced myoglobin —> etc.

Differs according to muscle: some high in MRA (longissimus dorsi), some low in MRA (biceps femoris)

(4) Cooked color problems
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.

(5) 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 reduced myoglobin and oxymyoglobin to metmyoglobin.

(6) Activity of bacteria

Pigment Catalyst New pigment
Oxymyoglobin

oxidation + bacteria

—————————->

Metmyoglobin (-OH)
Metmyoglobin

bacteria

—————————->

Choleglobin (-H2O2)
Metmyoglobin

bacteria

—————————->

Sulfmyoglobin (-SH)

(7) Curing

MyoglobinOxymyoglobinMetmyoglobin plus NO———> Nitric oxide myoglobin plus heat———> Nitrosylhemochromogen

(8) 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 on the Internet

 

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