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ANSC*2340 Conversion of Muscle to Meat
muscle fiber, rigor mortis, cold shortening, electrical stimulation
72
Anatomy
Undergraduate 2
03/09/2014

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Term
What does glycogen phosphorylase do?
Definition
initiates the release of chemical energy by breaking down glycogen
Term
What are the chemical products we see produced in stress-susceptible pigs, and their effects?
Definition
ATP & glucose-6-phosphate
-prevent phosphorylase from being activated in myofiber
Term
What is lost from the circulatory system after exsanguination?
Definition
-nutrient transport to muscles
-removal of waste & metabolites
-oxygen delivery
-heat removal
Term
After death, is the nervous system still functional in regards to muscle contraction?
Definition
-if an electrical impulse is provided the muscle fiber can still be stimulated
-NS is not truly working but the infrastructure is still present
Term
What is the primary goal of stunning?
Definition
to render an animal unconscious so that death can occur by exsanguination
Term
As long as O2 is available, how is ATP generated?
Definition
-metabolism of CHO, lipids, proteins
-ADP + phosphocreatine -> ATP & creatine
Term
What is the source of energy for converting creatine back to phosphocreatine?
Definition
using ATP produced in the Krebs Cycle
Term
When is the homeostatic mechanism of ATP production active?
Definition
when there is a high demand for ATP but oxygen is limited
Term
What is the product of anaerobic metabolism in the live animal?
Definition
lactic acid
Term
What is the fate of lactic acid in a live animal vs post mortem?
Definition
live: goes to heart (energy) or liver (glucose)

post mortem: stuck in myofibers
Term
True or False Anaerobic metabolism can continue post mortem
Definition
True, as long as glycogen is available and the cell environment is not too acidic
Term
What are the implications of lactic acid remaining in muscle cells post mortem? What effect does this have on the eating quality of meat?
Definition
-pH will decrease until glycolytic enzymes denature, & ATP production stops
-protein denature = less water holding ability = drier meat
Term
What is glycogen converted to so that anaerobic metabolism can take place post-mortem?
Definition
glycogen -> glucose 1 phosphate
Term
Why do we see an increase in body temperature after exsanguination?
Definition
-metabolic heat production
-slaughter process (scalding, singeing, hot water wash)
Term
What factors affect rise in temperature after exsanguination?
Definition
-rate of glycolysis
-size & location of muscles
-fat insulation
-fiber type
Term
What muscle fiber type will produce more heat and why?
Definition
white fiber because there is more anaerobic activity in these glycolytic fibers
Term
What is the result of not producing enough lactate in the conversion of muscle to meat?
Definition
DFD meat (dark firm dry)
Term
What is the result of producing too much lactate in the conversion of muscle to meat?
Definition
PSE meat (pale soft exudative)
Term
what causes PSE?
Definition
rapid rates of glycolysis decreasing pH too quickly & producing excess heat
Term
What causes protein denaturation in PSE?
Definition
increased carcass temperature & rapid rate of lactic acid production
Term
Sort the following species in decreasing order of the time required to complete the acidification process

Pigs
Turkey
Sheep
Cattle
Definition
Cattle
Sheep
Pigs
Turkey
Term
Will animals who had large stores of glycogen in their muscles prior to slaughter have a higher or lower ultimate pH after acidification has completed? Why?
Definition
lower pH because more glycogen = more substrates for lactic acid production = lower pH
Term
When is the conversion of muscle to meat complete?
Definition
-when the muscles' energy reserves are depleted

or

-when the muscles are unable to use remaining energy reserves
Term
What is required for the cycle of muscle contraction to repeat itself? What happens if this is not available
Definition
ATP & Ca2+

-myosin heads will remain locked to actin if ATP not available (X bridges are permanent)
Term
True or False

Passive filament sliding can still occur even if no ATP is available for muscle contraction
Definition
false
Term
What is the role of ATP in resting muscle?
Definition
forms a complex with Mg2+ and binds to the myosin head, preventing the formation of actomyosin
Term
How can muscle be stretched immediately after exsanguination?
Definition
adding a load/applying force to the muscle
Term
What happens if a load or force applied to a muscle immediately after exsanguination is removed?
Definition
natural elasticity returns the muscle to its resting length
Term
How many actomyosin bridges are present in a resting muscle that is being stretched?
Definition
very few, if any, because this muscle is resting
Term
What is the delay phase of rigor mortis?
Definition
the period after death when muscle is readily extensible & elastic
Term
How can ATP by synthesized after exsanguination?
Definition
using creatine phosphate + ADP, and then using glycogen stores to phosphorylate ADP
Term
What might affect the glycogen stores in a muscle?
Definition
how much stress or exercise the animal experienced prior to slaughter
Term
In the transition to rigor, what happens once actomyosin bridges form?
Definition
the muscle becomes less extensible if a load or force is applied
Term
What is the onset phase of rigor mortis?
Definition
when the muscle becomes less extensible
Term
As actomyosin bridges form, what is happening to the muscle?
Definition

-sarcomere length decreases

-thick & thin filaments overlap more

-muscle tension increases

-ATP levels decrease

Term
Why are xbridges permanent in rigor mortis?
Definition
because there is no ATP available to enable myosin heads to detach themselves from the binding site
(phosphocreatine & glycogen have been used up)
Term
When is rigor mortis complete?
Definition
when all binding sites between actin & myosin have actomyosin bridges
Term
Why can the body not get ride of the Ca2+ in muscle cells to relax the muscle?
Definition
no ATP available to pump Ca from sarcoplasm into SR
Term
Compare the number of xbridges formed in muscle contraction vs in RM
Definition
Muscle contraction: 20%
RM: 100%
Term
In the transition to rigor, ATP availability ______ and muscle extensibility _____ post-mortem
Definition
decreases ; decreases
Term
What is the rapid phase of rigor mortis?
Definition
running out of ATP on an individual muscle fiber basis, resulting in rapid loss of extensibility
Term
Why might Ca2+ leak from the SR and what would be the effect of this?
Definition
chilling effect on the muscle
-stimulates contraction
Term
If a small amount of glycogen is present, what effect will this have on the phases of rigor?
Definition
speeds up the onset
-not much ATP able to be produced

short rapid phase
-run out of ATP quickly
Term
If lots of glycogen is present, what effect will this have on the phases of rigor? Why?
Definition
delays the onset
-ATP is able to be produced

slow/drawn out rapid phase
-takes a while to run out of ATP
Term
Will a starved animal at slaughter have a long or short delay & rapid phase?
Definition
short delay, long rapid phase
Term
Will an exhausted animal at slaughter have a long or short delay & rapid phase?
Definition
short/no delay
very short rapid phase
Term
What causes RM to end?
Definition
lysosomal enzymes degrade the xbridges
Term
Why might you freeze meat prerigor?
Definition
improve water binding properties
enhance flavour
Term
What is thaw rigor?
Definition
Sudden release of Ca2+ when thawed results in massive contraction, rapid breakdown of ATP & onset of rigor, extensive muscle shortening
Term
Order the following meats in increasing order of delay time before onset of RM

Pork
Fish
Chicken
Lamb
Beef
Turkey
Definition
Chicken
Turkey & Fish
Pork
Beef & lamb
Term
Are all muscles affected the same by thaw rigor? Why/why not?
Definition
no

muscles attached to bone will show less shortening
Term
What is the effect of thaw rigor on meat quality?
Definition
tough, dry
Term
What is heat rigor?
Definition
rapid depletion of ATP stores & severe muscle shortening caused by muscle temperature reaching 50C before rigor develops
Term
When does cold shortening occur?
Definition
If the onset of rigor doesn't happen until the carcass is less than 10C
Term
What causes cold shortening?
Definition
release of Ca / failure to pump Ca into SR at lower temperatures, activates ATPase, causes contraction & decrease in sarcomere length
Term
What is more severe, cold shortening or thaw rigor?
Definition
thaw rigor
Term
True or False

Chilling has no effect on function of the SR
Definition
false
Term
Are the following species at high or low risk of cold shortening & why?

Pork
Poultry
Beef
Lamb
Definition
P&P: low risk, go into RM quickly
Beef: high risk, cool slowly & enter RM slowly
Lamb: very high risk, cool quickly & enter RM slowly
Term
What muscles would be affected more by cold shortening, red or white? Why?
Definition
red
-SR is less developed
Term
What is the effect of cold shortening on meat tenderness?
Definition
20-50% shortening will cause toughening of meat
Term
What is free water?
Definition
water that is not bound, will be easily lost during cooking
Term
How can you stop rigor contraction of unrestrained muscles?
Definition
-hanging the carcass by the aitch bone
Term
At what point during meat production would you use electrical stimulation to tenderize muscles?
Definition
before it enters the chill cooler
Term
Why is electrical stimulation not used on pork?
Definition
because it already goes into rigor quickly and has a fast rate of pH decline
Term
What is the effect of electrical stimulation on a carcass?
Definition
-increase rate of pH decline via glycolysis
-increase rate of RM development
-tenderizes the muscle
Term
Why does electrical stimulation speed up the development of rigor mortis?
Definition
-causes violent muscle contractions which uses up ATP quickly, and subsequently uses up glycogen stores
Term
How does electrical stimulation tenderize the muscle?
Definition
-prevents cold shortening
-disrupts myofiber structure
-increases release of Ca, calpain enzymes & lyososomal enzymes (proteolitic)
Term
What are calpains?
Definition
Ca2+ enzymes responsible for increasing post-mortem tenderization
Term
What are some other benefits of electrical stimulation, aside from tenderizing the meat?
Definition
-enhances colour & appearance (more red)
-increases firmness
-increases marbling visibility
-prevents formation of coarse bands
-increases flavour
Term
Is electrical stimulation effective on DFD beef? Why or why not
Definition
no
-already has low glycogen stores so won't benefit from increasing the rate of lactic acid production
Term
What level of voltage should be used for electrical stimulation right after death? Why?
Definition
low voltage
-direct stimulation of muscle contraction will increase the Ach being released, stimulating the sarcolemma
Term
What level of voltage should be used for electrical stimulation just prior to entering a chill cooler?
Definition
high voltage
-less Ach will be released at this point
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