Food Biochemistry and Food Processing (2 edition)

BLBS102-c16 BLBS102-Simpson March 21, 2012 10:54 Trim: 276mm X 219mm Printer Name: Yet to Come

308 Part 3: Meat, Poultry and Seafoods

Table 16.1.Physical Factors Affecting Proteolytic Activity During Meat and Meat Products Processing

Factor Typical Trend Effect on Proteases

pH Near neutral pH in dry-cured ham and

cooked meat products.

Favors the activity of calpain, cathepsins 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,

and fermented products

Short action for enough enzyme action 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

dry-curing

Enzymes have time enough for its activity even though 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 aw drops

Redox

potential

Anaerobic values in postmortem meat. Most of the muscle enzymes need reducing conditions for activity

Osmolality High in fast-twitch muscle. It may increase

from 300 to 550 mOsm within 2 d

Enhances proteases activity and these muscles are aged at faster

rate

and the heating/drying conditions during the fermentation and

ripening/drying affect protein solubility (Toldra and Reig 2007). ́

The reduction may reach 50–60% in the case of myofibrillar

proteins and 20–47% for sarcoplasmic proteins (Klement et al.

1974). There is a variable degree of contribution to proteolysis

by both endogenous and proteases and those of microbial origin.

This contribution mainly depends on the raw materials, the

type of product, and the processing conditions. The contribution

of microbial proteases to proteolysis also depends on the type

of strains. For instance, strainsStaphylococcus carnosusand

Staphylococcus simulanswere reported to hydrolyze sarcoplas-

mic but not myofibrillar proteins; however, no protease activity

was detected in another staphylococci but instead, some low

aminopeptidase and high esterase activity was found (Casaburi

et al. 2006).

The pH drop during the fermentation stage is very important.

So, when pH drops below 5.0, the proteolytic activity of endoge-

nous cathepsin D becomes very intense (Toldr ́a et al. 2001).

Several myofibrillar proteins, such as myosin and actin, are

degraded, and some fragments of 135, 38, 29 kDa, and 13 kDa

are formed. The major role of cathepsin D has been confirmed in

model systems using antibiotics and specific protease inhibitors

in order to inhibit bacterial proteinases or other endogenous

muscle proteinases (Molly et al. 1997). A minor role is played by

other muscle cathepsins (B, H, and L) and bacterial proteinases.

Peptides and small protein fragments are produced during

fermentation, heating (smoking), and ripening. The generation

of free amino acids, as final products of proteolysis, depends on

the pH reached in the product (as aminopeptidases are affected

by low pH values), concentration of salt (these enzymes are

Table 16.2.Chemical Factors Affecting Proteolytic Activity During Meat and Meat Products Processing

Factor Typical Trend Effect on Proteases

NaCl Low in aged meat No effect on enzyme activity

Medium concentration in cooked meat

products

Partial inhibition of most proteases except calpain

and aminopeptidase B that are

chloride-activated at low NaCl concentration.

High concentration in dry-cured hams Strong inhibition of almost all proteases

Nitrate and

nitrite

Concentration around 125 ppm in cured

meat products

Slight inhibitory effect on the enzyme activity,

except cathepsin B that is activated

Ascorbic acid Concentration around 500 ppm in cured

meat products

Slight inhibition ofm-calpain, cathepsin H, leucyl

aminopeptidase, and aminopeptidase B

Glucose Poor concentration in aged meat and dry-cured ham No effect

High concentration (up to 2 gL-1) in fermented

meats

Slight activation of leucyl aminopeptidase and

cathepsins B, H, and D