(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.
Hemoglobin -- transports O2 from lungs to cells
Myoglobin -- stores O2 in cells
(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
|Fe++ Ferrous (covalent)||:H2O||Purple||Reduced myoglobin|
|:NO||Cured pink||Nitric oxide myoglobin|
|Fe+++ Ferric (ionic)||-CN||Red||Cyanmetmyoglobin|
reduced myoglobin ---> oxymyoglobin ---> metmyoglobin ---> reduced myoglobin ---> etc.
Differs according to muscle: some high in MRA (longissimus dorsi), some low in MRA (biceps femoris)
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.
Myoglobin plus NO plus heat Oxymyoglobin ---------> Nitric oxide myoglobin --------->Nitrosylhemochromogen Metmyoglobin
Vacuum packages (polyvinylidene chloride-polyvinyl chloride); barrier to O2
Retail film (polyvinyl chloride); permeable to O2
(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.
Myoglobin HyperBase at W.M. Keck Center
Geometric Aspects of Protein Structure and Function
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