Meat Color

a water-soluble, globular protein that stores oxygen in muscle

What is myoglobin?

153

How many amino acids does myoglobin contain?

a single polypeptide chain with 8 alpha-helices

What is the structure of myoglobin?

a heme group with a central iron atom

What is the prosthetic group for myoglobin?

a porphyrin ring with 4 pyrrole nitrogen atoms

What is the heme ring of myoglobin made of?

6

How many binding sites does the heme iron have?

4 bind to the heme ring
1 binds to proximal histidine (His-93)

1 binds to ligands (O2, CO, H2O, NO)

What are teh 6 binding sites of the heme iron used for?

stabilizes O2 binding and reduced CO2 binding

What is the role of distal histidine (His-64)?

4 with 2 types (alpha and beta, delta, gamma, or epsilon)

How many polypeptide chains does hemoglobin have?

8 alpha chains

How many polypeptide chains does myoglobin have?

tetramer

What is the type of structure of hemoglobin?

monomer

What is the type of structure of myoglobin?

CO2, CO, NO, O2, and H+

What ligands bind to hemoglobin?

O2, tightly and firmly

What ligands bind to myoglobin?

all over the body; muscle cells

Hemoglobin is found ___ _____ _____ ___ while myoglobin is only found in ____ ____

transported with blood to whole body and carry oxygen

What is the role of hemoglobin?

supplying oxygen to muscles only

What is the role of myoglobin?

high; low

Hemoglobin is ____ in red blood cells; while myoglobin is ___ in red blood cells

myoglobin without oxygen bound

What is deoxymyoglobin?

ferrous (Fe 2+)

What is the iron state of deoxymyoglobin?

vacuum-packaged or uncut meat (no oxygen)
or right after slaughter

Where is deoxymyoglobin found?

very low oxygen partial pressure
only water to bind

Why does deoxymyoglobin form?

purplish-red

What color is deoxymyoglobin?

myoglobin bound to oxygen

What is oxymyoglobin?

ferrous (Fe 2+), unchanged

what is the iron state in oxymyoglobin?

greater than or equal to 40 tor O2 (around 5.25%)

Wha oxygen level is needed to form oxymyoglobin?

fresh, exposed (“blooming”) meat

overwrapped, Hi-Ox MAP

Where is oxymyoglobin found?

bright red (purplish-pink)

What color is oxymyoglobin?

no, it easily oxidizes to metmyoglobin (ferric Fe 3+)

Is oxymyoglobin stable?

oxidized form of myoglobin

What is metmyoglobin?

Ferric (Fe 3+)

What is the iron state in metmyoglobin?

brown

What color is metmyoglobin?

prolonged exposure to oxygen
deep layer of OMb without enough oxygen

When does metmyoglobin form?

low oxygen partial pressure
low metmyoglobin reducing activity (MRA)
bacterial oxygen consumption
oxidation of Fe 2+ to Fe 3+

What factors promote metmyoglobin formation?

5-10 mmHg (3.6-5.3%)

What is the partial pressure of oxygen in metmyoglobin?

0.2-1.3%

What is the cellular oxygen concentration in metmyoglobin?

Premature browning (safety issue)

development of well-done, internal cooked appearance at end-point temperatures lower than those needed to kill pathogenic bacteria

center

The endpoint temperature, pH, and predominate Mb (myoglobin) form in the ______ of the patty or steak at time of cooking

Persistent pink color (quality issue)

a pink/red color remaining after a safe endpoint temperature is reached
costly problem to meat produces and food service due to consumer rejection

$1 billion

meat discoloration = sales loss
What is the annual sales loss in the US?

oxidation of oxymyoglobin and metmyoglobin

What causes discoloration in meat?

it accelerates discoloration

How does lipid oxidation affect meat color?

oxidation caused by light (fluorescent lighting)

What is photooxidation?

metmyoglobin reducing activity (the ability to convert metmyoglobin back to myoglobin)

What is MRA?

using antioxidants

How can meat discoloration be prevented?

vitamin E, vitamin C, plant extracts, antioxidant-coated packaging

What are examples of antioxidants used in meat preservation?

it alters pH, leading to quality defects (PSE and DFD)

How does stress affect meat color?

Pale, Soft Exudative meat

What is PSE?

Dark, Firm, Dry Meat

What is DFD?

pork and poultry; beef

PSE is found in _____ ___ ______; DFD is found in _____.