muscle contraction and conversion to meat Flashcards
sarcomere is unit from
one Z disk to another
contractile unit of myofibril
4 most abundant components of myofibril
myosin 45%
actin 20%
tropomyosin 5%
troponin 5%
sliding filament theory
contraction occurring by sliding of thin filament i between thick filaments
I band contracts and A band gets denser
sequence of events of contraction (8)
nervous stimulation
depol of cell membrane
impulse transmitted to SR
release of Ca into SR
movement of thin filament
actin strands contact myosin heads
atp used to slide thin past thick
making and breaking cross bridge continues and atp is there
sequence of events of relaxation (6)
repolarization of cell membrane
Ca uptake into SR
tropomyosin shifts to block myosin binding site
atp regenerated
sarcomere return to resting length
first step in muscle to meat
rigor mortis development
2 stages of rigor development
early delay
rapid stage
early delay phase or rigor
using up ATP with continued contractions
glycolysis is giving creatine phosphate to supply energy
rapid rigor development phase
ATP production cannot keep up with demand for contraction, muscle fibers will lock in place
glycolysis trying to generate ATP makes lactic acid which decreased muscle pH
physical and chemical properties associated with rigor development
gradual reduction in muscle contraction
initial maintenance and then decline in muscle ATP levels
decline in muscle pH
implications for meat quality due to rigor
as rigor develops muscles shorted (contract) making them not as tender
3 types of muscle shortening
normal/heat shortening
cold shortening
thaw shortening
normal/ heat shortening
rapid fall in pH (<6) with muscle temp >35
as animal ages this will happen less
cold shortening
if muscle is chilled below 12 degrees and high pH >6
to avoid we want muscle pH <6 before temp drops below 12
cold shortened meat stays tough
only issue in beef and sheep
thaw shortening
occurs when frozen pre rigor muscle is thawed
can be dramatic (50-80%)
very tough after cooking
pre rigor muscle vs rigor muscle vs post rigor muscle
pre rigor-reversibly stretches under light pressure
rigor- reluctantly reversible stretched at greater loads
post rigor- readily irreversibly stretched under light loads
rigor and aging
aging is the process of rigor muscle slowly relaxing
when does chilled muscle become flaccid
3-4 days post mortem at chill tempuratures
when is max toughness post slaughter
24 hr
at 1 degree C when do you reach 80% reduction in toughness
10 days post slaughter
calpain proteolytic system
Ca dependent
attacks Z discs
inhibited by calpastatin
cathepsins
lysosomes released post mortem to degrade troponin and some collagen links
making more tender
post slaughter handling and processing
carcass chilling
electrical stimulation
carcass chilling
controls rate of microbial spoilage and minimized heat or cold shortening effects
blast chill then holding cooler at 0-3
electrical stimulation
accelerated rigor development by increasing rate of glycolysis
increases rate of post mortem pH decline and atp usage rate
improves meat tenderness by prevents pre rigor toughening of meat that is chilled or frozen
also converts myoglobin to oxymyoglobin improving meat colour (brighter)
mechanisms of electrical stimulation
prevention of cold shortening by early rigor development
increase activity of proteolytic enzymes due to rapid pH decline
physical rupture of muscle fibers du to massive contractions
dark cutter pH
6.0-6.8
why is dark cutter meat dark
hindered conversion to oxymyoglobin
canadian grade for dark cutter
b4
dark cutter meat
muscle glycogen is depleted due to stress
most common in late summer and early fall
risk factors include aggressiveness, estrus, stress, growth promotants, hot weather
consequence of high muscle pH meat
stimulates growth of spoilage bacteria reducing shelf life
causes of dark cutter
transportation exhaustion
hunger/feed withdrawl
fear and stress
aggressive behaviour
exercise
high temp
how long do glycogen reserves take to replenish
3d
