postmortem glycolysis and glycogenesis

after slaughter, ate metabolism continues briefly, H+ release, pH drops glycogen becomes lactate, producing acidity and pH drop

slower pH fall and higher ultimate pH

the rate and extent of pH fall depends on

muscle glycogen concentration at slaughter

factors influencing pH decline and meat quality

genetics nutrition environment handling and transport large (rest period before slaughter) immobilisation (stunning method) chilling temp and rate

which muscle fibres have less glycogen

Type I (slow twitch) often have high ultimate pH

biochemical causes of dark cutting (DFD) meat

insuffiecient glycogen low glycolytic potential stress transport extreme temps feed withdrawal

myoglobin and meat colour chemistry

myoglobin carries O2 via Fe in heme core postmortem O2 depletion stops reduction reactions and oxidation occurs ROS form mitochondria to oxidise myoglobin

DFD meat myoglobin behaviour

high ultimate pH, slow pH decline mitochondria stay active longer, high O2 use, more deoxymyogllobin

PSE meat myoglobin behaviour

fast pH drop and high temp post-slaughter mitochondria lose activity rapidly unstable Fe3+ mletmyoglobin forms

leads to stress glycogen depletion DFD risk

high cortisol, lactate and glucose

long trips lead to fatigue and glycogen loss

allows recovery must include water, feed and space

porcine stress syndrome (PSS)

genetic disorder linked to Ryr1 gene mutation causes uncontrolled Ca2+ release, increased metabolism (hyperthermia)

sudden death muscle rigidity PSE from rapid pH fall

Green meat and myoglobin degradation

caused by bacterial sulfur byproducts reacting with myoglobin to create sulfmyoglobin (green pigment)

Deep pectoral myopathy (DPM)

affects tenderloin poor blood supply causes ischaemia, infmallation and necrosis

stress noise water restriction heavy wing weight (muscles grown too big)

white fat streaks along pectorals major fibres caused by repeated atrophy/regeneration cycles

affects pectoralis major caused by degeneration, inflammation and fibrosis related to poor connective tissue and reduced capillary density

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Animal phys L8

Question	Answer
postmortem glycolysis and glycogenesis	after slaughter, ate metabolism continues briefly, H+ release, pH drops glycogen becomes lactate, producing acidity and pH drop
Low glycogen	slower pH fall and higher ultimate pH
the rate and extent of pH fall depends on	muscle glycogen concentration at slaughter
factors influencing pH decline and meat quality	genetics nutrition environment handling and transport large (rest period before slaughter) immobilisation (stunning method) chilling temp and rate
main energy source postmortem	glycogen
which muscle fibres have less glycogen	Type I (slow twitch) often have high ultimate pH
biochemical causes of dark cutting (DFD) meat	insuffiecient glycogen low glycolytic potential stress transport extreme temps feed withdrawal
myoglobin and meat colour chemistry	myoglobin carries O2 via Fe in heme core postmortem O2 depletion stops reduction reactions and oxidation occurs ROS form mitochondria to oxidise myoglobin
ROS	Reactive oxygen species
deoxymyoglobin	low O2 purple/red colour
oxymyoglobin	high O2 bright red
metmyoglobin	oxidised brown/grey
DFD meat myoglobin behaviour	high ultimate pH, slow pH decline mitochondria stay active longer, high O2 use, more deoxymyogllobin
PSE meat myoglobin behaviour	fast pH drop and high temp post-slaughter mitochondria lose activity rapidly unstable Fe3+ mletmyoglobin forms
poor handling	leads to stress glycogen depletion DFD risk
stress indicators	high cortisol, lactate and glucose
transport stress	long trips lead to fatigue and glycogen loss
Large (rest period)	allows recovery must include water, feed and space
porcine stress syndrome (PSS)	genetic disorder linked to Ryr1 gene mutation causes uncontrolled Ca2+ release, increased metabolism (hyperthermia)
PSS results in	sudden death muscle rigidity PSE from rapid pH fall
Green meat and myoglobin degradation	caused by bacterial sulfur byproducts reacting with myoglobin to create sulfmyoglobin (green pigment)
Deep pectoral myopathy (DPM)	affects tenderloin poor blood supply causes ischaemia, infmallation and necrosis
DPM triggered by:	stress noise water restriction heavy wing weight (muscles grown too big)
White striping	white fat streaks along pectorals major fibres caused by repeated atrophy/regeneration cycles
woody brest	affects pectoralis major caused by degeneration, inflammation and fibrosis related to poor connective tissue and reduced capillary density

Created by: sakelleher29

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