Post-mortem Handling of Carcasses and Meat
Quality
Ante-mortem Slaughtering
Post-mortem
The way the carcass is
processed
Meat quality
T E M P E R A T U R E
Cold shortenin
g
Heat ring
Thaw rigor Heat shortenin
g
Carcass Chilling
• At death, animals have a body temperature of between about 37 and 39°C.
• After carcass dressing the temperature drops as heat is lost to the surrounding air.
size of the carcass
the covering of subcutaneous fat
the circulation of air over the surface
Normal practice is to achieve a meat
temperature of 7°C or
below before further
handling such as butchery,
or transport from the plant
• In conventional chilling systems the carcasses are placed in chill rooms held at about 1°C as soon as possible after they have been dressed, washed and inspected.
Because of the large amount of hot
carcass meat, and therefore the large amount of heat that needs to be
dissipated, the air temperature in the chiller may rise above 1°C for
periods while hot carcasses are being loaded
Chilling ProcessChilling Process Refrigerated air
Reduce microbial growth on the carcass surface and to reduce evaporative weight
losses.
Refrigerated air
Reduce microbial growth on the carcass surface and to reduce evaporative weight
losses.
E.coliE.coli
35°C divides every 25 min
whereas at 7°C the
generation time is
more than 25 h.
35°C divides every 25 min
whereas at 7°C the
generation time is
more than 25 h.
Weight LossWeight Loss
2-3 % of carcass weight in normal chilling to less than 1% over the first 24 h of
storage.
2-3 % of carcass weight in normal chilling to less than 1% over the first 24 h of
storage.
PSEPSE Reduce the manifestation of PSE pork, improving
water-holding capacity
(WHC) and lean
color.
The influence of
temperature on muscle metabolism
Speed of onset of rigor
mortis.
The
disappearance of creatine phosphate and
ATP
The rates of
pH fall
• The rate of pH fall depends on the muscle temperature.
• The minimum rate occurs at about 10°C.
• As the temperature gets closer to 0°C the rate increases.
• Also, as the temperature increases to 37°C the rate increases
The rate of pH fall in beef muscles is approximately linear with time.
overall a curvilinear relationship between rate of pH fall and
temperature
Activation of the actomyosin ATP-ase
The increase below 10°C is caused by a calcium dependent
ATP-ase The increase above
10°C is caused by increasing activation
of calcium-
independent ATP-ase
Cold shortening
Occurs when the muscle is cooled below about 10°C before the onset of rigor.
Most acute in situations where rigor development is delayed and where small volumes of tissue are being chilled.
Because of too quick chilling, SR is unable to hold the calcium
Muscle contraction occurs while ATP still is avaliable
Pig&Chicken
Cattle
Lamb
Species
such as chickens and pigs, because they have relatively rapid rates of rigor onset, are less prone to cold shortening even though their
carcasses are small (Møller and Jensen, 1993). Beef carcasses tend to cool slowly because of their bulk and are again less prone.
Lamb
carcasses are small enough to cool rapidly and generally do not enter rigor quickly. They are therefore most prone to shortening
Different muscles in the carcass will also be differently predisposed to cold shortening because of inherent
metabolic differences. So, while the m. longissimus dorsi is very prone to cold shortening, the m. psoas is hardly affected
In normal beef, cold shortening can be prevented by ensuring that muscle temperature does not fall below 10°C until the muscle pH has reached 6.1, which would normally take about 10 h. By this time, the progress of rigor will be sufficiently advanced to
prevent cold contracture.
Heat Ring
• The phenomenon of so-called ‘heat ring’
sometimes occurs in beef subjected to relatively fast chilling.
• Found in carcasses with a thin rind.
• In particular, the parts nearer the outside of the carcass cools more quickly than the inside so the rate of pH fall is reduced.
• This leads to a darker band of muscle forming. This
has an unattractive appearance.
Thaw Rigor
• If the rate of cooling of the carcass is sufficiently high and the meat freezes before the onset of rigor then, on thawing, the muscle shortens severely (to up to 50% of its length if unrestrained) and becomes very tough after cooking.
• Additionally, very large amounts of drip or exudate
(30 % of muscle weight) are lost during thawing.
On thawing, glycolysis is completed very rapidly
and ATP breakdown is extremely rapid
This rapid metabolism is accompanied by a very
strong contraction
The contraction is probably stimulated by
the rapid and massive release of calcium ions
from the sarcoplasmic reticulum on thawing
