Postmortem Changes in Muscles

oxygen concentration, pH, temperature, energy supply

What are some of the physiological conditions maintained in homeostasis?

maintain; efficiently; homeostasis

In the living state, all organs and systems within teh body interact to ______ an environment under which each can perform its functions ______. Maintenance of this physiological state is termed ______.

removal of blood or exsanguination

what marks the beginning of postmortem changes?

drop in blood pressure and the activation of homeostatic control mechanisms

What happens in response to the removal of blood or exsanguination?

protecitive/survival insticnt that compensates for blood loss

What is the purpose of the homeostatic control mechanisms especially after exsanguination?

increase in heart rate to maintain circulation, peripheral vessels contrict to prioritize blood flow, 50% of remaining blood redirected to vital organs

What homeostatic control mechanisms kick in after severe blood loss or exsanguination?

oxygen concentration, pH, temperature, energy

What are the four major factors affecting homeostasis?

organs

During a severe loss of blood in animals, where is the remaining blood redirected to?

(muscles or organs?)

less blood and oxygen to muscle
lack of oxygen causes switch to anaerobic metabolism (respiration)

What is the result of the homeostatic controls mechanism caused by blood loss?

metabolism stops

Muscle is not converted to meat until:

TCA cycle and electron transport failing

What is the result of decreased oxygen concentration?

Anaerobic Metabolism

when lacking oxygen
mostly glycolysis
less energ-sufficient
accumulation of lactic acid

glycogen

Anaerobic metabolism continues until ______ stored in the muscle is depleted?

accumulation of lactic acid

What is responsible for the postmortem muscle pH changes?

greatly variable

Is the rate of decline in muscle pH consistent or variable?

meat quality

pH is a major part of:

water holding capacity

What does muscle pH also affect?

doesn’t hold as much water

If the muscle pH is closer to the isoelectric point, the muscle:

changes in meat quality attributes (color, protein functionality, tenderness, juiciness)

What are the consequences of pH decline?

ATP binds to myosin/actin bond and detaches the molecules; needs ATP to pump Ca to its destination

How does muscle fiber use ATP during contraction?

no

Is anaerobic metabolism the only thing that affects postmortem pH change?

the breakdown of ATP to ADP and phosphate through hydrolysis produces hydronnium ions (H+) that affects pH

What affects muscle pH besides the lactic acid build up from anaerobic metabolism?

not at the beginning, but it completely depletes over time

Is oxygen completed depleted postmortem (in muscles)?

Myoglobin

What is responsible for the color of meat?

mainly due to loss of water so myoglobin is more concentrated and more red

How does pH decline affect the color of the meat?

100%; 20%

In rigor mortis, ____ of binding sites are used
In normal contraction, ____ of binding sites are used

microbial growth, protein denaturation, oxidation

What are the consequences of pH decline and temperature rise on meat?

Glycotic/anaerobic metabolism and creatine phosphate

What are the two sources of ATP?

muscle contraction and metabolism

What are two things that ATP is used for in relation to the meat industry?

rigor sets when ATP depletes

What is the consequence of postmortem energy changes?

stiffness of death

What is Rigor Mortis also called?

immediately after exsanguination

When is the delay phase of Rigor Mortis?

within hours, species dependent

When is the Onset phase of Rigor Mortis?

within 24 hours, specie dependent

When is the Completion phase of Rigor Mortis?

Delay Phase

Immediately after death, ATP is still plentiful in muscles. Relaxation is possible because ATP is sufficient to power the dissociation of actomyosin. The muscle remains soft.

Onset Phase

As oxygen stops flowing, ATP production shifts to anaerobic glycolysis and quickly depletes, along with creatine phosphate (used to make more ATP). As ATP levels drop, actin-myosin cross-bridges form and cannot break, leading to muscle stiffening.

Completion Phase

ATP stores are virtually exhausted. Muscles become completely rigid as the actomysoin complex is permanently fixed.

all of them

How many binding sites are used at Rigor completion?

shortened

What is the length of the sarcomeres at rigor completion?

the maximum stiffening of muscle fibers

What is the muscle tension at rigor completion?

irreversible and permanent bonds

What is special about actomyosin bonds at rigor completion?

6-12 hours

What is the delay time before onset of rigor mortis for beef?

6-12 hours

What is the delay time before onset of rigor mortis for lamb?

1/4-3 hours

What is the delay time before onset of rigor mortis for pork?

<1 hours

What is the delay time before onset of rigor mortis for turkey?

<1/2 hour

What is the delay time before onset of rigor mortis for chicken?

<1 hour

What is the delay time before onset of rigor mortis for fish?

Resolution

decrease in tension with time postmortem

no

Are the actomyosin bonds broken in resolution?

proteolysis (enzymatic degradation of muscle structural proteins)

What happens in resolution that makes the meat tender?

48-72 hours post-mortem

When is the most notable change in muscle structure integrity after death?

starts subtle degradation right after exsanguination

When do the changes in muscle structure integrity actually start?

desmin, titin, nebulin

What proteins are broken down when the Z disks are degraded?

Titin

What is the primary protein broken down in postmortem muscle changes that results in a decrease in passive elasticity?

tenderness, flavor, color, juiciness

What qualities are altered during the aging of meat?

tenderness

What quality is altered most in the aging of meat?

Actin and Myosin

What proteins are not degraded?

enzymatic activities, specifically postmortem proteolytic degradation of myofibril proteins

What causes the resolution of rigor mortis?

myofibril proteins are broken down by proteolytic enzymes

What happens to muscle proteins during resolution of rigor?

the Calpain system

Which enzyme system is mainly responsible for postmortem proteolysis?

Calcium-dependent proteolytic enzymes involved in muscle protein degradation after death

What are Calpains?

cytoplasm of muscle cells

Where are Calpains located?

micro-calpain, m-calpain, Calpastatin (inhibitor)

What are the components of the Calpain system?

a calpain enzyme activated at at millimolar (high) calcium concentrations

What is m-calpain?

a calpain enzyme activated at micromolar (low) calcium concentrations

What is micro-calpain?

a specific inhibitor protein that regulations calpain activity

What is calpastatin?

calcium ions released from the mitochondria and SR

What activated calpain postmortem?

during postmortem storage (aging)

When does proteolysis occur during meat processing?

it is only slightly degraded during aging

What happens to connective tissue after death?

the become slightly degraded

What happens to cell membranes postmortem?

• Loss of membrane integrity leads to fluid leakage (drip loss)

• Affects water-holding capacity

• Impacts texture and juiciness

Why is cell membrane degradation important for meat quality?

It fails and no longer functions

What happens to the lymphatic system after death?

• it can no longer remove pathogens or toxins

• Microorganisms are free to spread throughout tissues

Why is lymphatic system failure important for meat safety?

They stop functioning and can no longer defend against microbes

What happens to circulating white blood cells postmortem?

Due to loss of protective biological systems and barriers

Why does microbial risk increase after death (besides temperature)?

Movement of microorganisms from initial contamination sites to other tissues

What does “spread” refer to in postmortem meat?

Rapid multiplication of microorganisms in the tissue

What does “proliferation” mean in the context of meat safety?

Introduction of microorganisms from external sources (equipment, environment, handling).

What does “contamination” refer to in meat processing?

spread, proliferation, contamination

What are the three key microbiological risks postmortem?

7; 5.5

Postmortem, due to the change of glycogen to lactic acid, the muscle pH drops from ___to___.

disruption of transverse cross-linking between myofibrils an leads to fragmentation of myofirbils

What does the degradation of desmin cause?