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

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

 

(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) 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.

(5) Activity of bacteria

oxidation + bacteria Oxymyoglobin----------------------------> Metmyoglobin (-OH) bacteria Metmyoglobin----------------------------> Choleglobin (-H2O2) bacteria Metmyoglobin----------------------------> Sulfmyoglobin (-SH)

(6) Curing


Myoglobin 	plus NO 			plus heat

Oxymyoglobin  ---------> Nitric oxide myoglobin --------->Nitrosylhemochromogen

Metmyoglobin

(7) 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

Myoglobin HyperBase at W.M. Keck Center
Geometric Aspects of Protein Structure and Function


Meat Science at Texas A&M University

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