Unit 12 - Conversion of Muscle into Meat and Meat Quality Flashcards
How DFD meat occur?
no decline of pH
- stressed preslaughter (long-term)
- glycogen stores are used up because of constant stress so when they are slaughtered, there is no more glycogen, therefore no lactate produced postmortem, and therefore the pH remains high
- observed more in beef
How does PSE meat occur?
sudden drop in pH postmortem
- stressed preslaughter (short-term)
- causes breakdown of glycogen for fight or flight and the system is triggered to produce lots of lactate and as the animal is being slaughtered, this causes the continuation of lactate production, therefore large drop in pH
- the thing that actually causes PSE is the denaturation of the proteins in the muscle due to acidity (low pH) mixed with the fact that the carcass body temp is very hot
- seen in pork
What is WHC?
water holding capacity - of myofibre proteins
What is pl?
isoelectric point (number of - and + charges are equal)
Explain the Meat pH vs WHC graph
pl of the majority of the myofibrillar proteins is approx 5.1-5.4
at the isoelectric point - the + and - charged groups within a protein attract each other and the ability of the protein to attract and hold water is minimal
high WHC when pH is high or low
What happens to WHC during postmortem?
declines during postmortem decrease the availability on the muscle proteins that bind water
How does preslaughter stress occur?
release of stress hormones such as epinephrine
once released these hormone initiate a series of biochemical reactions designed to mobilize energy to meet the demands of the stressors
What does epinephrine activate?
glycogen phosphorylase which enhances glycogen breakdown
What is the activation process of the body during acute stress?
acute stress (short-term) -> accelerates the glycogenolysis -> rapidly declines pH
What is the activation process of the body during chronic stress?
chronic stress (long-term) -> anticipate the glycogen consumption -> lack of sources for glycolysis postmortem
What are two conditions associated with low muscle temperature prior to onset rigour?
thaw rigour
cold-shortening
happen because of the same mechanism but happen differently
How does cold temperature affect meat quality?
lowering the temperature will cause changes in the capacity of SR to control the Ca2+ in the sarcoplasm, the sarcoplasm becomes overloaded with Ca, more Ca in sarcoplasm, more contractions
if it occurs before the glycogen is depleted, a more severe contraction will occur
more contraction affects the tenderness
What occurs to cause thaw rigour?
- occurs when muscle is frozen before going into rigor, then thawed
- during freezing: ice crystals grow and penetrate the sarcoplasmic reticulum. Subsequent thawing of the crystals enables a rapid release of Ca2+ into the sarcoplasm
- upon thawing the muscle, Ca is rapidly released causing a massive contraction (because ATP is produced due to presence of glycogen)
this causes an increase in meat toughness
What occurs to cause cold shortening?
- less severe than thaw rigor and occurs when muscle is chilled to less than 14 C before rigor
- low temp prompts Ca release from sarcoplasmic reticulum, and at colder temps, the SR Ca ATPase cannot bind and resequester Ca effectively
- resulting increase in cytosolic Ca concentration in the presence of ATP leads to muscle contraction and shortening
- increase in meat toughness - less severe than thaw rigor
What makes a carcass more susceptible to cold shortening?
- red muscle is more susceptible to cold shortening than white muscle
- red muscle has less developed SR
- more subcutaneous fat insulates carcass and prevents drop in temp so carcasses with less subcut fat will be more susceptible
- cold shortening is not seen in pig carcass
How to prevent cold shortening
use of electrical stimulation, accelerations glycolysis and ATP utilization -> permits onset of rigor to occur (burning through of glycogen) earlier and at greater temps than those that induce cold shortening
- when carcass enter cold environment, less glycogen will be available to produce ATP
- although calcium will be released in sarcoplasm, it won’t affect contraction intensity due to lack of ATP
Explain the graph showing lower pH in stimulated muscle at slaughter
lower pH in the first hour of a carcass that was stimulated shows that glycogen is being depleted to prevent cold shortening
What is proteolysis
process of breaking proteins into peptides
When is the aging time for meat?
between the slaughter and the meat consumption
Where does aging typically occur?
under refrigeration at 4C
Is aging of meat good?
yes, it is necessary to improve meat tenderness
How does aging cause better tenderness?
caused by proteolysis -> breakdown of proteins into smaller constituents comprised of polypeptides or AA
as meat ages, structural changes occur in myofibril, one of the changes is the breakage or structural damage near the Z-line band in the sarcomere are targeted by enzymes
What causes proteolysis in aging of meat?
proteases (enzymes) that are naturally present in muscle
- have access to structural proteins in the sarcomere
Where are proteases for proteolysis found?
localized within the skeletal muscle
