14 Biochemistry of Processing Meat and Poultry 323in sarcoplasmic proteins. The patterns for myosin
heavy chain, myosin light chains 1 and 2, and tro-
ponins C and I show a progressive disappearance
during the processing (Toldrá et al. 1993). Several
fragments of 150, 95, and 16 kDa and in the ranges
of 50–100 kDa and 20–45 kDa are formed (Toldrá
2002). The analysis of ultrastructural changes by
both scanning and transmission electron microscopy
shows weakening of the Z-line as well as important
damage to the fibers, especially at the end of salting
(Monin et al. 1997). An excess of proteolysis may
create unpleasant textures because of intense struc-
tural damage. The result is a poor firmness that is
poorly rated by sensory panelists and consumers.
This excess of proteolysis is frequently due to the
breed type and/or age, which have a marked influ-
ence on some enzymes, or just a higher level of
cathepsin B activity (Toldrá 2004a). A high residual
cathepsin B activity and/or low salt content, a strong
inhibitor of cathepsin activity, are correlated with
the increased softness. The action of calpains is re-
stricted to the initial days of processing due to their
poor stability. Cathepsin D would contribute during
the initial 6 months, and cathepsins B, L, and H,Table 14.1.Physical Factors Affecting Proteolytic Activity during Meat and Meat Product
Processing
Factor Typical Trend Effect on Proteases
pH Near neutral pH in dry-cured ham and Favors the activity of calpain, cathepsins
cooked meat products B and L, DPP III and IV, TPP II, and
aminopeptidases
Slightly acid in aged meat Favors the activity of cathepsins B, H,
and L
Acid pH in dry-fermented sausages Favors the activity of cathepsin D, DPP I,
DPP II and TPP I
Time Short in aged meat, cooked meat products, Short action for enough enzyme action
and fermented products except for calpains that contribute to
tenderness
Medium in dry-fermented sausages Time allows significant biochemical
changes
Long in dry-cured ham Very long time for important biochemical
changes
Temperature High increase in cooking and smoking Enzymes are strongly activated by
cooking temperatures, although
stability decreases rapidly and time of
cooking is short
Mild temperatures in fermentation and Enzymes have time enough for their
dry curing activity even with the use of mild
temperatures
Water activity Slightly reduced in cooked meats Enzymes have good conditions for
activity
Substantially reduced in dry meats Restricted enzyme activity as awdrops
Redox potential Anaerobic values in postmortem meat Most of the muscle enzymes need
reducing conditions for activity
Osmolality High in fast-twitch muscle; may increase Enhances proteases activity, and these
from 300 to 550 mOsm within 2 days muscles are aged at faster rate