Meat Science Exam 3

Homeostasis

maintenance of all organs and systems in the body interacting to maintain an environment under which each can perform its function efficiently

narrow rang of physiological conditions includes what?

oxygen concentration, pH, temperature, and energy supply

What marks the beginning of postmortem changes?

removing blood or exsanguination

What happens after removing blood?

blood pressure drops, homeostatic control kicks in, increase heart rate, constricted peripheral vessels, and 50% blood redirected to vital organs

What is muscle converted to meat?

when metabolism stops

What occurs when oxygen is depleted?

TCA cycle and electron transport fail

What is homeostatic maintenance shift due in the beginning of postmortem?

anaerobic metabolism

Anaerobic

lack oxygen, uses glycolysis, and accumulates lactic acid

How long does anaerobic metabolism last?

until glycogen stored in muscle is depleted

What causes decline of muscle pH?

accumulated lactic acid and CO2

ATP hydrolysis

oxygen deficiency

calcium ion pump

Algo Mortis

brief stabilization or slight increase of temperature followed by steady decline until body matches ambient environment

What are the factors of postmortem temperature changes?

rate of metabolism

size/ location of muscles

predominance muscle fiber type

fat insulation

duration of metabolism

If pH declines and temperature rises, what occurs?

microbial growth, protein denaturation, and oxidation

What are the 2 sources of ATP postmortem?

glycolytic/ anaerobic metabolism and creatine phosphate

How is ATP used postmortem?

muscle contractions and metabolism

When does rigor set in?

when ATP is depleted and there is stiffness of death

Delay phase of rigor

occurs immediately after exsanguination/ loss of blood

Onset phase of rigor

occurs within hours of slaughter but is species dependent

Completion phase of rigor

occurs within 24 hours after slaughter

What occurs at rigor completion to myosin, sarcomere, muscle tension, and actomyosin?

myosin is bound to actin, sarcomere length shortens making muscle stiff, muscle tension reaches its max, and actomyosin are stable

What breaks down muscle fibers?

enzymes and collagen/ connective tissue

Resolution to rigor mortis

stiff muscle relaxes and become flexible after death caused by decomposition and breakdown of muscle tissue

Calpain system

2 calcium-dependent enzymes with an inhibitor activated by calcium release from mitochondria and sarcoplasmic reticulum during storage

m-calpain

millimolar high calcium concentration

μ-calpain

micromolar low calcium concentration

Calpastain

inhibitor of calpains that plays vital role in regulating protein turnover and protecting cells from uncontrolled degradation

Stress

physiological adjustments that occur during exposure of animal to adverse conditions

What are the adverse conditions of stress?

stressors

What are consequences of stress in the muscle?

increased demand for muscle contractions

stress hormones have to help meet muscle demand

production of lactic acid leaves muscle

PSE

pale soft and exudative meat

What happens with rapid pH decline?

short-term stress before slaughter seen in pigs

What happens with slow pH decline?

long-term stress at expense of glycogen store in ruminants

DFD

dark, firm, and dry meat

Water holding capacity

ability of meat to retain naturally occurring or added water during application of external forces like cutting, heating, grinding, or pressing

What physical properties depend on WHC?

color, exture, firmness, binding, and pH

What is change of meat when it comes to WHC?

negative

What are methods of immobilization?

CO2, electric shock, captive bolt, electric stunning, and rapid bleeding

What happens if we lower carcass temps.?

prevention of protein denaturation, enzyme/ microbial activities, and microbial/ bacterial growth

Thaw rigor

severe rigor caused by thawing muscle that was frozen

What does thaw rigor do?

it causes sudden release of calcium ions into sarcoplasm and physical shortening of unrestrained muscle

Cold shortening

sudden shortening pre-rigor caused by nervous stimulation induced by cold temps.

Heat ring

lean carcasses like ribeye is chilled too fast causing low glycolytic metabolism and high pH

What shoudl we do to prevent pre-rigor?

salt meat within 2-3 hours post-mortem preventing rigor and protein degradation

Myoglobin

water-soluble protein, has single polypeptide chain, has 153 a.a., 8 a-helix sections, and has prosthetic heme group with an iron atom in the center

Iron II - ferrous - oxygen

red in color = oxymyoglobin

Iron II - ferrous - water

purple in color = reduced myoglobin

Iron II - ferrous - NO

pink in color = nitric oxide myoglobin

Iron II - ferrous - CO

red in color = carboxymyoglobin

Iron III - ferric - OH

brown in color = metymyoglobin

Iron III - ferric - H2O2

green in color = choleglobin

Iron III - ferric - NO

brown in color = nitric oxide metmyoglobin

Oxymyoglobin

bright red pigment formed when myoglobin in muscle tissue binds with oxygen without a change to iron’s valence

Metmyoglobin

oxidized form of myoglobin causing meat to turn a brown or gray-brown color occurring as meat ages

Cooked meat color

myoglobin + heat —> denaturation —> pH and temp —> red to pink to tan to brown color

Premature browning

ground beef turns brown and appears fully cooked at internal temps below 160 degrees

Persistent pinking

pink/ red color remaining after safe endpoint temp. is reached

What are some remedies for raw meat color preservation?

feed supplements to animals like Vit. E, preserves can be sprayed on meats like Vit. E & C, and active packaging or antioxidant coated film

Is pH lower or high in darker raw meat?

it is lower