2009_Book_FoodChemistry

596 12 Meat
Table 12.18. Oxidative fat deterioration in cooked beef
Beef
Raw Cooked Cured a Cured and cooked a
Non-heme iron (µg/g) 6.62 10.8 6.65 6.80
Storage at 4 ◦ C Malonic aldehyde (mg/kg) b
0. Day 0.58 0.56
5. Day 1.55 0.48
12. Day 2.78 0.47
21. Day 2.83 0.54
a Cured with 156 mg/kg nitrite.
b Determined with the thiobarbituric acid test.
blast freezer with an air temperature of −40 ◦ C
and an air stream velocity of 3–10 m/s. The shelf
life for storage at −18 ◦ Cto−20 ◦ C and 90%
relative humidity is 9 to 15 months. The shelf life
of frozen chicken, as affected by storage temperature,
is presented in Fig. 12.29, while Table 12.17
shows the deterioration of frozen chicken as it is
shipped from producer to consumer. The shelf life
is largely determined by oxidative changes affecting
the lipids, which take place more readily in
poultry (ducks, geese, chickens) and pork than in
beef or mutton.
The water holding capacity of frozen meat
increases as the freezing temperature decreases.
Fig. 12.29. Shelf life of frozen chicken as affected by
storage temperature. — Shelf life A, −−−quality loss
B = 100/A (according to Gutschmidt, 1974)
Water holding capacity also remains high when
freezing is performed rapidly. Under these
conditions the formation of large ice crystals
is suppressed and damage to membranes and
the irreversible change in myofibrillar proteins
caused by temporary high salt concentrations are
avoided.
Freezing meat immediately after slaughtering,
without precooling (single-stage process), causes
substantial shortening and high fluid losses on
thawing, if the meat freezes completely before
rigor occurs. However, this is possible only with
smaller cuts. The reason for this phenomenon is
an extremely fast ATP breakdown with a corresponding
decrease in the water holding capacity.
The sudden high rate of ATP breakdown is
initiated by release of Ca 2+ ions from the
sarcoplasmic reticulum, which triggers the high
activity of myosin-ATPase (“thaw rigor”). This
“thaw rigor”, which is associated with toughness,
can be avoided if the warm meat is frozen and
then minced in the frozen state after addition
of NaCl. Thaw rigor may also be avoided by
disintegrating warm meat in the presence of NaCl
and then freezing it.
Freezing matured meat results in lower fluid
losses than freezing meat in a prerigor or rigor
state. However, this process is not widely used
for economic reasons. Rigor can be induced
before freezing by using electrical stimulation.
Long storage of frozen meat results in a decrease
in water holding capacity. Solubility changes
and shifts in the isoelectric point of proteins
of the sarcoplasm and contractile apparatus are
observed.