Lecture 31: Meat quality

Breaking down Z line

Done by proteases

Naturally present in muscle

Larger effect during post mortem

Specific proteases involved in meat tenderization

Calpain/Calpastatin system

Proteasome and caspase system

Protease: Calpains

Endogenous protease

Need Ca²⁺ for activity

Mew Calpain binds to 5-8 Ca ions

M calpain binds to 11-20 Ca ions

Optimal temp for best activity is 25 to 30 degrees celcius

pH for activity is 7

Inhibited by Calpastatin

Protease: Calpastatin

Endogenous proteases

Also need Calcium ions for activity

Inhibits calpain by preventing calpain proteolytic activation

Causes conformational change in calpains and blocks active sites

Tenderness evaluation: Warner Bratzler Shear Force

Assessing tenderness differences within given round muscle

Little loss of accuracy

Tenderness evaluation: Sensory panel testing

Methods for assessing tenderness differences based on individual perceptions

Aging and proteolysis

Instrumental measures of meat tenderness decreases

Measures of intensity of myofibrillar protein breakdown increases

Meat colour

Primary quality trait evaluated by final consumer when purchasing

Factors of meat colour evaluation

Subjectively by meat graders

Instrumentally

Instrumental colour evaluations: a, b and L

L = whiteness

a = redness

b = yellowness

Instrumental colour evaluation: Negative values

a = intensity of green light reflectance

b = intensity of blue light reflectance

L = dark not much light reflectance

Instrumental colour evaluation: Positive values

a = intensity of red light reflectance

b = intensity of yellow light reflectance

L = higher intensity of light reflectance

Meat colour: Myoglobin

Varies depending on animal’s age

Muscles from older animals have more myoglobin contractions than younger animals

Why the meat is more tough, less tender

What affects myoglobin solubility

High temps and low pH

Causes denaturation of myofibrillar proteins

Cause denaturing of myoglobin

Decrease redness of meat

Lack of Oxygen

Iron is not bound to gas

High concentrations of deoxymyoglobin

Meat looks darker

Vacuum packaged meat

Lots of oxygen and iron in ferrous state

High affinity for oxygen

Form of myoglobin that is responsible for bright red colour

Observed in traditional retail meat packages

Oxygen permeable wrap

Both deoxymyogloin and oxymyoglobin

Iron ion remains in ferrous state (2+)

Change in colour is due to lack of oxygen

No changes in state of iron (stays 2+)

Metmyoglobin

Oxidation of heme iron results in transition from ferrous iron (2+) to ferric iron (3+)

Ferric iron does not have a high affinity for oxygen

Makes meat gray/brown

Why metmoglbin occurs

When meat has been exposed to environment for long period of time

Catalyzed by high temperature

Negatively impact retail sales