98 Chapter 4
chain fragments, myosin light chain II, and
triose phosphate isomerase at 72 hours post-
mortem correlate to shear force measure-
ments at 1 and 4 days postmortem in porcine
longissimus muscle (Lametsch et al. 2003 ).
Similarly, spots corresponding to actin, myo-
kinase, F - actin capping protein, HSP27,
myosin light chain I, peroxiredoxin 2, trios-
ephosphate isomerase, and troponin T were
correlated to shear force changes between 1
and 7 days postmortem in porcine longissi-
mus muscle (Hwang et al. 2005 ). In longis-
simus muscle from Korean native cattle,
researchers identifi ed seven proteins that are
differentially expressed in samples from
carcasses segregated into high - and low - qual-
ity beef grades (based on marbling, lean
color, fat color, maturity, and tenderness)
(Kim et al. 2008 ). Both HSP27 and inositol
1,4,5 - triphosphate (IP3R1), which is involved
in the intracellular pathways that mediate
Ca 2+ release from intracellular stores
(Berridge and Lipp 2000 ), were higher in
low - quality beef, and HSP27 was positively
correlated to 2 - day postmortem shear force
measurements.
Proteomic studies on postmortem muscle
have led to new insights into the mechanisms
of aging tenderization in meat. Based on
studies using one - dimensional SDS - PAGE, it
has been accepted for years that actin is not
degraded postmortem (Bandman and Zdanis
1988 ; Huff - Lonergan et al. 1995 ; Koohmaraie
1994 ). Several studies using 2DE separation,
however, have demonstrated that fragments
of actin accumulate with postmortem storage
(Lametsch et al. 2002 ; Lametsch et al. 2003 ;
Morzel et al. 2004 ; Hwang et al. 2005 )
and that the abundance of actin fragments
correlates to tenderness (Lametsch et al.
2003 ; Hwang et al. 2005 ). Similarly, these
studies have also observed that fragments of
myosin accumulate with postmortem storage
(Lametsch et al. 2002, 2003 ; Morzel et al.
2004 ). While aging tenderization is usually
thought to be a manifestation of changes toFrom these studies, myofi brillar proteins or
fragments of myofi brillar proteins found to
change with postmortem storage include
actin, myosin heavy chain, titin, myosin
light chain I, myosin light chain II, CapZ,
cofi lin, troponin - T, cypher proteins, and
myozenin. Sarcoplasmic proteins enolase,
phosphoglycerate kinase, pyruvate dehydro-
genase, glycogen phosphorylase, triosephos-
phate isomerase, myokinase, eukaryotic
translation initiation factor 5A, α - crystallin,
creatine kinase, and pyruvate kinase were
also found to change with postmortem
storage in these studies (Lametsch et al.
2003 ; Morzel et al. 2004 ). Using a model in
which isolated myofi brils were incubated
with μ - calpain under simulated postmortem
conditions and protein degradation was mea-
sured by combining MALDI - TOF MS with
SDS - PAGE and 2DE, one study observed
that desmin, actin, myosin heavy chain,
myosin light chain I, troponin - T, tropomyo-
sin, thioredoxin, and CapZ were degraded in
vitro by μ - calpain (Lametsch et al. 2004 ). In
both bovine longissimus and semitendinosus
muscles, levels of cofi lin, lactoylglutathione
lyase, substrate protein of mitochondrial
ATP - dependent proteinase SP - 22, HSP27,
and HSP20 were found to be different
between samples removed at 0 and 24 hours
postmortem (Jia et al. 2006 ). This study also
found 15 additional proteins that changed
during postmortem storage in either the lon-
gissimus or semitendinosus muscles (Jia et al.
2006 ). In a similar study, thirty - nine proteins
were identifi ed from bovine longissimus
muscle that signifi cantly change during the
fi rst 24 hours postmortem (Jia et al. 2007 ).
Proteins undergoing changes included meta-
bolic enzymes, cellular - defense and stress -
response proteins, structural proteins, and
proteolytic enzymes.
Some of the proteomic changes observed
during postmortem aging have been corre-
lated with tenderness measurements. The
abundance of actin fragments, myosin heavy